Aftermarket Li battery components

[Don Y]

Hi,

A friend just gave me a couple of "expansion batteries"
for my tablet PC's. Of course, the batteries are flat.
*And*, of course, they won't take a charge. :<

Pulling one open, there are 4 (5?) batteries that
appear to be identical distributed around the case
(the battery pack is very thin but as tall and wide
as the tablet).

Is it worth trying to replace these with some comparable
cells? (I am sure the vendor of the original expansion
pack would charge a heavy premium to put those cells in
this large plastic shell and resell it! :> )

What other issues might I have to worry about?

Or, is it better to just live with the standard (working)
batteries and discard the expansion batteries?

Thx,
--don

 

[mike]

Hi,

A friend just gave me a couple of "expansion batteries"
for my tablet PC's. Of course, the batteries are flat.
*And*, of course, they won't take a charge. :<

Pulling one open, there are 4 (5?) batteries that
appear to be identical distributed around the case
(the battery pack is very thin but as tall and wide
as the tablet).

Is it worth trying to replace these with some comparable
cells? (I am sure the vendor of the original expansion
pack would charge a heavy premium to put those cells in
this large plastic shell and resell it! :> )

What other issues might I have to worry about?

Or, is it better to just live with the standard (working)
batteries and discard the expansion batteries?

Thx,
--don

This is a complex issue.
Words like "flat" and "won't take a charge" may be clear in
your mind, but don't communicate much.

I've spent considerable time working on this issue.

The executive summary is, "give it up and go do something fun."

If you're gonna mess with this, there are some ground rules.

WEAR EYE PROTECTION.
DO NOT SKIP THIS STEP. I'VE HAD NiCd BATTERIES EXPLODE AND
SPRAY HOT CAUSTIC STUFF IN MY FACE.

Don't let your kids watch.
Don't leave it unattended.
Have an EMPTY metal trash can handy and a clear path to outdoors.
Make sure your fire insurance is paid.
Have a working fire extinguisher handy. It won't do much for
a lithium fire, but might keep the whole house from going up.

NEVER, NEVER, NOT EVER SHOULD YOU SOLDER DIRECTLY TO A BATTERY.
Repeat that until you believe it. Don't let anybody tell you otherwise.
Let them blow up their laptop if they want.

My experience is mostly with packs over 5 years old. Protection
circuitry becomes progressively more sophisticated.

I've experienced two failure modes.
1)cell is open. The pressure switch has opened and they ain't coming back.
2)High internal resistance. The amp-hours are in there, but the protection
circuit or the laptop won't let you take it out.

Of course it's possible that your cells are good and have just
overdischarged
and the electronics have disconnected 'em.

You've got it open, check the voltage of each cell. If it's over
2.5V, you can probably charge each one individually to some higher
voltage. 3.8V seems like a safe number. You want them all MATCHED
at the same voltage. That's my definition of "take a charge".
If the voltage is lower, there's higher risk that charging them will
start a fire.
I've recharged cells at low current from less than one volt, but I never
left it unattended.

Whether you've managed to recharge existing cells or replaced them,
you face the electronics problem.

The battery chip may have lost power. Its response varies.
I never got any thinkpad chip to let me restart the battery.
I managed to restart one NiCd battery that had a PIC processor
by resetting the PIC.
Dell C-series batteries come back, but when you press the test button,
you get a flashing light pattern. The laptop battery light flashes
continuously...but they seem to work ok.

Another wrinkle is that the battery remembers its current capacity.
If you replace the cells, it's likely that the memory contains the old
number and may not let you have more than that capacity. There are ways
to reset that, but it's a secret closely guarded by the battery rebuild
people.

If I'd spent all the time I spent working on this issue working at the
corner
burger joint at minimum wage, I could have easily purchased new batteries
for every laptop I've ever owned and still be money ahead.

Are we having fun yet?

 

[Don Y]

Hi Mike,

This is a complex issue.
Words like "flat" and "won't take a charge" may be clear in
your mind, but don't communicate much.

Sorry, flat == 0.00volts. To be more explicit, each cell
shows 0.00 volts. "Flat".

And, of course, they *won't* take a charge in that condition!

I've spent considerable time working on this issue.

The executive summary is, "give it up and go do something fun."

Taking things apart to learn stuff is *fun*.

If you're gonna mess with this, there are some ground rules.

WEAR EYE PROTECTION.
DO NOT SKIP THIS STEP. I'VE HAD NiCd BATTERIES EXPLODE AND
SPRAY HOT CAUSTIC STUFF IN MY FACE.

Don't let your kids watch.
Don't leave it unattended.
Have an EMPTY metal trash can handy and a clear path to outdoors.
Make sure your fire insurance is paid.
Have a working fire extinguisher handy. It won't do much for
a lithium fire, but might keep the whole house from going up.

NEVER, NEVER, NOT EVER SHOULD YOU SOLDER DIRECTLY TO A BATTERY.
Repeat that until you believe it. Don't let anybody tell you otherwise.
Let them blow up their laptop if they want.

My experience is mostly with packs over 5 years old. Protection
circuitry becomes progressively more sophisticated.

I've experienced two failure modes.
1)cell is open. The pressure switch has opened and they ain't coming back.
2)High internal resistance. The amp-hours are in there, but the protection
circuit or the laptop won't let you take it out.

I wasn't able to see anything on each cell. Some shared electronics
to which everything attaches. Plus a couple of temperature sensors
(?) sitting atop a couple of the cells.

Of course it's possible that your cells are good and have just
overdischarged
and the electronics have disconnected 'em.

You've got it open, check the voltage of each cell. If it's over
2.5V, you can probably charge each one individually to some higher
voltage. 3.8V seems like a safe number. You want them all MATCHED
at the same voltage. That's my definition of "take a charge".

My definition is "the pack won't even try to push current into
the cells" :>

If the voltage is lower, there's higher risk that charging them will
start a fire.
I've recharged cells at low current from less than one volt, but I never
left it unattended.

I'm more interested in *replacing* as (to me) they are obviously
long past the point of no return.

Whether you've managed to recharge existing cells or replaced them,
you face the electronics problem.

The battery chip may have lost power. Its response varies.
I never got any thinkpad chip to let me restart the battery.
I managed to restart one NiCd battery that had a PIC processor
by resetting the PIC.

I didn't notice what was on the board in the battery. I'll be
more observant next time I open one up.

Dell C-series batteries come back, but when you press the test button,
you get a flashing light pattern. The laptop battery light flashes
continuously...but they seem to work ok.

Another wrinkle is that the battery remembers its current capacity.

Ah, good point!

If you replace the cells, it's likely that the memory contains the old
number and may not let you have more than that capacity. There are ways
to reset that, but it's a secret closely guarded by the battery rebuild
people.

Then, I guess it depends on what that "number" happens to be!

If I'd spent all the time I spent working on this issue working at the
corner
burger joint at minimum wage, I could have easily purchased new batteries
for every laptop I've ever owned and still be money ahead.

If you measure happiness with money, that may well be the case!

Are we having fun yet?

Actually, yes! :>

"A dollar picked up in the road is more satisfaction to you
than the ninety-and-nine which you had to work for..."
--Twain

I'll see if I have any salvaged 18650's and tie them in with some
clipleads and see if the pack shows any signs of life, if the
tablet recognizes it, etc. Costs nothing to try! And, based on those
results, see what sorts of cells are available in that form factor.

Thanks!

 

[mike]

Hi Mike,



Sorry, flat == 0.00volts. To be more explicit, each cell
shows 0.00 volts. "Flat".

And, of course, they *won't* take a charge in that condition!


Taking things apart to learn stuff is *fun*.


I wasn't able to see anything on each cell.

The pressure sensor is inside the positive terminal
Some shared electronics

to which everything attaches. Plus a couple of temperature sensors
(?) sitting atop a couple of the cells.


My definition is "the pack won't even try to push current into
the cells" :>

There's several places in the "pack" where the charge can be interrupted.
You have to try to stuff current directly into the cell.
If the cell won't take any current at all, it's likely
popped the pressure sensor.

I'm more interested in *replacing* as (to me) they are obviously
long past the point of no return.


I didn't notice what was on the board in the battery. I'll be
more observant next time I open one up.

Probably a charge control fet, a discharge control fet a processor chip
various sensor taps on each cell that may or may not go directly to the
processor,
temperature sensor thermistor, thermal fuse,
some means of talking to the computer probably I2C clock and data.

Ah, good point!

There's a windows program called PCWizard that can talk to the internal
pack and tell you what
the number is. But it may fail to communicate if the pack is completely
dead and won't power the comm interface.

The wording of the original post suggests that these might be batteries
that are added in addition to the internal pack. PCWizard probably
can't talk to those...and much of what I've said might not apply.

Then, I guess it depends on what that "number" happens to be!


If you measure happiness with money, that may well be the case!

Or you could measure happiness with the free time you get from using
that money to save time and frustration charging batteries...all the
while consuming delicious burgers and
learning Spanish.

Actually, yes! :>

"A dollar picked up in the road is more satisfaction to you
than the ninety-and-nine which you had to work for..."
--Twain

Maybe for half a minute. When it comes time to pay the mortgage,
I'll take the ninety-and-nine.

 

[miso]

FWIW, I rebuilt a pack in an instrument that used 18650s. Of course I
bought them new and had them electro-welded. I'm not all that keen on
spending time and energy with salvaged batteries. You have a task to do,
you buy the parts, fix it, and get on with business.

I will repeat the other persons post about not soldering to batteries.
In the words of Grand Master Flash, "Don't Do It!"

 

[Don Y]

FWIW, I rebuilt a pack in an instrument that used 18650s. Of course I
bought them new and had them electro-welded. I'm not all that keen on
spending time and energy with salvaged batteries. You have a task to do,
you buy the parts, fix it, and get on with business.

Salaged batteries can be perfectly usable -- depending on the
device into which you install them!

E.g., I pulled an 18650 out of a discarded battery pack taking care
to keep the long "tabs" that had been welded onto the cell to
connect it to it's neighboring cells. These were ideal to connect
to in the single cell GPS unit to which I installed it! If *that*
cell ever dies, I would gladly repeat the exercise -- since buying
a new cell would necessitate paying someone to weld tabs onto it!

 

[mike]

Salaged batteries can be perfectly usable -- depending on the
device into which you install them!

E.g., I pulled an 18650 out of a discarded battery pack taking care
to keep the long "tabs" that had been welded onto the cell to
connect it to it's neighboring cells. These were ideal to connect
to in the single cell GPS unit to which I installed it!

Well...yes, but that's not what you asked about.
A GPS is a much less demanding application.
One cell is MUCH easier to manage.
Low current evokes fewer problems with cell ESR.


If *that*

cell ever dies, I would gladly repeat the exercise -- since buying
a new cell would necessitate paying someone to weld tabs onto it!

Yep, my DIY tab welder helps a lot.

You can buy cells with tabs welded on.
I found that, in many laptop battery cases, they cut the plastic so
close that there's
not enough room to overlap two tabs and solder them.

 

[Don Y]

Hi Mike,

The pressure sensor is inside the positive terminal

OK. Assuming the sensor *opens* the circuit to the battery
(and doesn't self-reset), that would account for seeing 0.00V
on *each* cell (I can drag out a better DVM to verify it really
has "zero potential").

But, what are the odds of all 8 cells (4 batteries in each battery
pack) having *that* same problem at the same time?

(I can check the other battery packs to see what their symptoms
are. I suspect they have just "run flat" over time)

There's several places in the "pack" where the charge can be interrupted.
You have to try to stuff current directly into the cell.

I hesitate with the cells *all* claiming to be (completely) flat.
If there was signs of life on one or more, I might try to coax
them back to life...

If the cell won't take any current at all, it's likely
popped the pressure sensor.

Again: *all* of them? (and, possibly, all in the other battery
packs, as well? Design flaw?)

Probably a charge control fet, a discharge control fet a processor chip
various sensor taps on each cell that may or may not go directly to the
processor,
temperature sensor thermistor, thermal fuse,
some means of talking to the computer probably I2C clock and data.

That sounds about right. I'll drag out the stereoscope and take
a closer look (my eyes are too old, otherwise :> )

There's a windows program called PCWizard that can talk to the internal
pack and tell you what
the number is. But it may fail to communicate if the pack is completely
dead and won't power the comm interface.

The wording of the original post suggests that these might be batteries
that are added in addition to the internal pack.

Correct. These are "extended battery packs" or "expansion battery
packs" or somesuch. I.e., the tablets operate off a standard
battery but capacity can be augmented by attaching one of these
(very different form factor, etc.)

PCWizard probably can't
talk to those...and much of what I've said might not apply.


Or you could measure happiness with the free time you get from using
that money to save time and frustration charging batteries...all the
while consuming delicious burgers and learning Spanish.

I measure happiness by how many new things I learn and how
challenging obtaining that information happens to be!
Tonight, I learned how the brain processes "pleasurable
experiences". (someday, I may actually *understand* what
I've learned! :> )

Learning another language at my age would be WAY too
frustrating and of very little reward. ("Gee, if we
were to hire some latinos I could speak to them in their
native tongue!" "Yes, or you could try English!")

And burgers have been losing their appeal for many years,

Maybe for half a minute. When it comes time to pay the mortgage,
I'll take the ninety-and-nine.

I guess it depends on whether you *have* a mortgage, or not!

I actually found the quote rather insightful. Its amusing to
consider how something as "insignificant" can bring a
disproportionate amount of pleasure!

I'll open the battery packs -- a couple of them so I can verify
the symptoms of each -- tomorrow or next week and see what else
turns up. I suspect I will have to coax the cells out of the
case (double-sided tape) so I can really see what's up...

 

[Don Y]

Hi Mike,

On 4/21/2012 10:56 PM, Don Y wrote:

Yep, my DIY tab welder helps a lot.

You can buy cells with tabs welded on.
I found that, in many laptop battery cases, they cut the plastic so
close that there's
not enough room to overlap two tabs and solder them.

I won't bother trying to rebuild a laptop battery. Easier to
just run them off AC. There's already lots of cruft that
accompanies the laptop (well, at least *my* laptops) like
power supply, power cord, network cable, USB cable, minihub,
WiFi sniffer, etc. So, carrying the power adapter doesn't
seriously impact the amount of bulk you're dragging along
with it.

OTOH, the tablets are much smaller and can benefit from
*not* needing any of that cruft. But, then you rely on
the battery, more!

If push comes to shove and the "normal" expansion battery
interface won't accommodate my repairs, I can always tether
the battery to the "DC inlet" that the power adapter normally
feeds.

 

[mike]

Hi Mike,


OK. Assuming the sensor *opens* the circuit to the battery
(and doesn't self-reset), that would account for seeing 0.00V
on *each* cell (I can drag out a better DVM to verify it really
has "zero potential").

Instead of a pressure sensor, let's call it a non-resettable circuit
breaker actuated by internal cell pressure.

But, what are the odds of all 8 cells (4 batteries in each battery
pack) having *that* same problem at the same time?

That was my reaction too. I've got packs where the breaker
in every cell was tripped. Only explanation I can come up with is
that the cells overheat and there's some delay before the pressure
builds to the trip point.

Measuring the cell voltage is inconclusive. If the voltage is zero,
you could put your meter on diode test to see if they're open or really
zero. I use a current-limited power supply for the test.

(I can check the other battery packs to see what their symptoms
are. I suspect they have just "run flat" over time)


I hesitate with the cells *all* claiming to be (completely) flat.
If there was signs of life on one or more, I might try to coax
them back to life...


Again: *all* of them? (and, possibly, all in the other battery
packs, as well? Design flaw?)

Yep, I've seen 'em all tripped.

That sounds about right. I'll drag out the stereoscope and take
a closer look (my eyes are too old, otherwise :> )


Correct. These are "extended battery packs" or "expansion battery
packs" or somesuch. I.e., the tablets operate off a standard
battery but capacity can be augmented by attaching one of these
(very different form factor, etc.)


I measure happiness by how many new things I learn and how
challenging obtaining that information happens to be!
Tonight, I learned how the brain processes "pleasurable
experiences". (someday, I may actually *understand* what
I've learned! :> )

Learning another language at my age would be WAY too
frustrating and of very little reward. ("Gee, if we
were to hire some latinos I could speak to them in their
native tongue!"

I was thinking more about latinas.
"Yes, or you could try English!")

And burgers have been losing their appeal for many years,


I guess it depends on whether you *have* a mortgage, or not!

I actually found the quote rather insightful. Its amusing to
consider how something as "insignificant" can bring a
disproportionate amount of pleasure!

I'll open the battery packs -- a couple of them so I can verify
the symptoms of each -- tomorrow or next week and see what else
turns up. I suspect I will have to coax the cells out of the
case (double-sided tape) so I can really see what's up...

That tape can be really tough. Try to bend the case and not the
battery. I've punctured cells trying to get 'em out.

 

[Don Y]

Hi Mike,

On 4/22/2012 5:11 AM, Don Y wrote:

Instead of a pressure sensor, let's call it a non-resettable circuit
breaker actuated by internal cell pressure.

OK. "Vent"

That was my reaction too. I've got packs where the breaker
in every cell was tripped. Only explanation I can come up with is
that the cells overheat and there's some delay before the pressure
builds to the trip point.

Hmmm... OK, I'll buy that. Sort of like a tea kettle "whistling"
after being removed from the heat (if timed *just right*)

Measuring the cell voltage is inconclusive. If the voltage is zero,
you could put your meter on diode test to see if they're open or really
zero. I use a current-limited power supply for the test.

I'll try that.

Yep, I've seen 'em all tripped.

OK. I'll check the first battery pack before opening up any of
the others (less risk of cosmetic damage to *all* if I just
concentrate on one.)

I was thinking more about latinas.

Ah! My other half would frown on that sort of motivation! :>
Women tend to have pretty strong feelings on these things...
(go figure!)

That tape can be really tough.

Yes. When I initially tried to remove one, I grew alarmed at
how much stress I was putting on the cell. The fact that the
cells are soft-sided and so "thin" and "wide" makes them even
more susceptible to mechanical abuse.

(each is about the size/shape of the original iPod and perhaps
1/8" thick -- yet, covered with double-sided tape on the one
side!)

Try to bend the case and not the
battery. I've punctured cells trying to get 'em out.

If the cells are toast (you haven't claimed the "pressure vent"
is resettable!), then I'm not worried about their "value",
rather, any paste getting out!

 

[mike]

Hi Mike,



OK. "Vent"

Ok, I see where this discussion has gone horribly astray.
I got fixated on your mention of 18650's and have been talking about
that. And it seems that "flat" applied to the cell geometry as well
as their charge level.
AFAIK, the 18650, used in the majority of laptops, has a pressure
switch under the positive terminal that opens when some target pressure
is reached.
The purpose is to prevent venting and thermal runaway. I'm sure there
is a vent, but it's
probably at much higher pressure. I've never found any sign of venting
debris around a cell that was open-circuit.

If you have flexible cells that look like plastic baggies, there's no way
to contain pressure.
All my experience was with single-cell PDA batteries. The safety problem
is much simpler with one cell. I've replaced them without incident.
Just have to cut the plastic at the end and take out the little board
and put it on the new cell.

I have seen PDA cells swell up to the point that you can't get the case
back together.

It's not clear how your cells are connected. Five is an odd number that
suggests they all have to be in series. That voltage is too high.
If it's four cells, the logical connection is two cells tall and two
wide. I'd expect they'd need the same type of balance protection that
is used in laptop batteries. But I have zero experience there.

Hmmm... OK, I'll buy that. Sort of like a tea kettle "whistling"
after being removed from the heat (if timed *just right*)


I'll try that.


OK. I'll check the first battery pack before opening up any of
the others (less risk of cosmetic damage to *all* if I just
concentrate on one.)


Ah! My other half would frown on that sort of motivation! :>
Women tend to have pretty strong feelings on these things...
(go figure!)


Yes. When I initially tried to remove one, I grew alarmed at
how much stress I was putting on the cell. The fact that the
cells are soft-sided and so "thin" and "wide" makes them even
more susceptible to mechanical abuse.

More confusion. I've punctured metal 18650's trying to get them
off the tape. They're certainly not intended to come out.
Soft-sided cells are considerably more delicate.
I've never tried to re-use one I've pulled out of a pack.
That makes it difficult to scavenge cells from other packs.

(each is about the size/shape of the original iPod and perhaps
1/8" thick -- yet, covered with double-sided tape on the one
side!)


If the cells are toast (you haven't claimed the "pressure vent"
is resettable!),

People claim to have reset the pressure switch on 18650's by stuffing
a tool thru the hole in the positive terminal. I gave it a try, but
was unsuccessful at pressures I was willing to exert. There's risk of
puncturing the top of the cell. Even if it works, you might be left
with a cell shorted by your tool and risk of explosion. Not worth the risk.

then I'm not worried about their "value",

rather, any paste getting out!

I guess the key is whether they're individually protected
or go to some common protection scheme.

Measure right at where the protected cell attaches to the product and again
between the protection and the terminals coming out of the cell...
depending on the configuration.

You've got to determine where the protection is.

 

[Don Y]

Hi Mike,

Ok, I see where this discussion has gone horribly astray.
I got fixated on your mention of 18650's and have been talking about

Sorry, my fault. I mentioned 18650's in the context of (temporarily)
wiring in four of them to replace the existing cells (based solely
on cell voltage, nothing mechanical) to test if the "number" that
the battery pack "remembers"/reports is likely to give me a useful
battery pack in the future *if* I can successfully replace the "dead"
cells with functional ones "having the correct mechanical
characteristics"

that. And it seems that "flat" applied to the cell geometry as well
as their charge level.
AFAIK, the 18650, used in the majority of laptops, has a pressure
switch under the positive terminal that opens when some target pressure
is reached.
The purpose is to prevent venting and thermal runaway. I'm sure there is
a vent, but it's

Ah, OK. So the switch *responds* to pressure *before* the
cell would otherwise vent or rupture...

probably at much higher pressure. I've never found any sign of venting
debris around a cell that was open-circuit.

If you have flexible cells that look like plastic baggies, there's no way
to contain pressure.

These aren't as "soft" as some of the cells that I've seen
but they are nowhere near as "rigid" as an 18650. I.e.,
I suspect if I "poked" one with my finger, I could easily
deform/short it (?)

All my experience was with single-cell PDA batteries. The safety problem
is much simpler with one cell. I've replaced them without incident.
Just have to cut the plastic at the end and take out the little board
and put it on the new cell.

These individually tie in to a "set of conductors" (flex circuit)
that runs between them. Not abutting end-to-end as is common
in laptop battery packs. I.e., if replacement cells had similar
length tabs (~1/2 - 1") it would be a lead-pipe cinch to replace
them!

I have seen PDA cells swell up to the point that you can't get the case
back together.

It's not clear how your cells are connected. Five is an odd number that
suggests they all have to be in series. That voltage is too high.

Five was a misremembered figure. There are a total of eight
cells in the "battery". It appears they are arranged as
four groups of two (14.8V). But, I can't say for sure
if each set of two are *directly* connected together (which
is what it appears, superficially) or if there is another
"layer" in the flex circuit that allows each cell to connect to
the "controller board" independently.

I.e., it appears that there are only *8* connections to the controller
board (4 x 2). Removing the board is tough as the flex circuit
ties it to all of the cells and effectively acts as a mechanical
restraint holding the board in place.

If it's four cells, the logical connection is two cells tall and two
wide. I'd expect they'd need the same type of balance protection that
is used in laptop batteries. But I have zero experience there.

I will open it up and gently poke around the individual cells.
I can't tell if there are two or *three* conductors coming off
each as teh connections to the flex circuit are difficult to
follow without disturbing things.

More confusion. I've punctured metal 18650's trying to get them
off the tape. They're certainly not intended to come out.

Oh, OK. Yes, 18650's are more massive and tend to have less surface
area so the tape seems to be more agressive. These are much larger
(probably 6 sq inches on a side) so the adhesive needn't be as
tough. But, there's a lot *more* of it! Sort of like having
a square foot of velcro proves to be a daunting task to
separate while a little piece pulls apart easily.

Soft-sided cells are considerably more delicate.
I've never tried to re-use one I've pulled out of a pack.
That makes it difficult to scavenge cells from other packs.

I'm not averse to buying new cells -- assuming they are
available, affordable and *needed*. OTOH, I don't want
to make a *career* out of this...

People claim to have reset the pressure switch on 18650's by stuffing
a tool thru the hole in the positive terminal. I gave it a try, but
was unsuccessful at pressures I was willing to exert. There's risk of
puncturing the top of the cell. Even if it works, you might be left
with a cell shorted by your tool and risk of explosion. Not worth the risk.

So, would you expect a similar sort of "switch" in these
flat, soft-sided cells? Or, is that meaningless -- because
it would be difficult to direct the pressure to a relief
point? (i.e., 18650's are confined in a rigid case, these
aren't)

I guess the key is whether they're individually protected
or go to some common protection scheme.

Measure right at where the protected cell attaches to the product and again
between the protection and the terminals coming out of the cell...
depending on the configuration.

You've got to determine where the protection is.

OK. I'll get a bit more aggressive in my probing...