Extending the Life of a Rechargable Battery

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Ive heard its better for the life of a battery to charge a battery to
full capacity, use it until it drains completely and then fully
recharge it and so on. I heard the battery will go bad faster if you
partially charge, discharge more frequently. Is this true? Does it
depend on the type of rechargable battery?

 

[Jim Thompson]

Ive heard its better for the life of a battery to charge a battery to
full capacity, use it until it drains completely and then fully
recharge it and so on. I heard the battery will go bad faster if you
partially charge, discharge more frequently. Is this true? Does it
depend on the type of rechargable battery?

NiCad are worst for that. Most other types aren't so sedative to
discharge depth.

...Jim Thompson

 

[Joerg]

Hello Jim,

NiCad are worst for that. Most other types aren't so sedative to
discharge depth.

Yes, but AFAIK NiCd are the only ones that can be trickle charged. NiMH
supposedly doesn't like that, making stand-by applications rather
cumbersome (meaning more $$$) in terms of charger circuitry.

Regards, Joerg

 

[Martin Riddle]

A discharged battery has the potential to grow dendrites (whiskers) between the plates. Some formulas are better than others, Lead
acid and NICAD are at the top of the list.
Shocking Nicads tend to burn off the dendrites, but they eventually grow back.

Cheers

 

[kell]

Ive heard its better for the life of a battery to use it until it drains completely

for some batteries, yes. Just don't drain a lead acid battery. Bad
for it.

 

[Robert Baer]

Ive heard its better for the life of a battery to charge a battery to
full capacity, use it until it drains completely and then fully
recharge it and so on. I heard the battery will go bad faster if you
partially charge, discharge more frequently. Is this true? Does it
depend on the type of rechargable battery?

*NO* battery "likes" to be fully discharged!
That being said, the NiCd cells have a "memory" problem, and the only
way to "reset" that is to do an almost complete discharge and then
charge; sometimes this is needed moer than once for recovery.
So, this regimen to "reset" their memory theoretically reduces their
lifetime - but without the "reset" they are useless anyway, making the
theory un-proveable and moot.
Other uses that can shorten cell lifetime is heavy discharge and
heavy, un-controlled charging.
Roughly, a cell should not be discharged to less than 80 percent of
rating, and the discharge rate should not be greater than C/2 or only
"bursts" of C *if* the chemistry supports that.

 

[Keith Williams]

*NO* battery "likes" to be fully discharged!

Not true. NiCds and NiMH batteries can be fully discharged, but not below 0V
on any cell. A multi-cell NiCd battery may reverse charge a weak cell which
*will* kill it. NiCds should be stored discharged (but self-discharge is good
too).

OTOH, lead-acid batteries must never be fully discharged. Deep discharging
them tends to warp the plates causing shorts. "Marine" batteries have thicker
plates (thus lower power-density and higher internal resistance) and are less
susceptible to plate warping.

That being said, the NiCd cells have a "memory" problem, and the only
way to "reset" that is to do an almost complete discharge and then
charge; sometimes this is needed moer than once for recovery.
So, this regimen to "reset" their memory theoretically reduces their
lifetime - but without the "reset" they are useless anyway, making the
theory un-proveable and moot.

The "memory" problem isn't. It's much legend about a totally different issue
(one that has been pretty much non-existent for 20 years).

Other uses that can shorten cell lifetime is heavy discharge and
heavy, un-controlled charging.

Over-charging and reverse charge during discharge are by far the most common
cause of early failure of NiCds.

Roughly, a cell should not be discharged to less than 80 percent of
rating, and the discharge rate should not be greater than C/2 or only
"bursts" of C *if* the chemistry supports that.

Not less than 80% of rating? Nonsense. Lead-acids shouldn't be discharged
below 20%, perhaps. NiCds can be run to down to zero as long as the cells
don't reverse polarity.

You'd better talk to model airplane nuts and electric drill manufacturers about
your C/2 or C "rule".

 

[Rich Grise]

*NO* battery "likes" to be fully discharged! That being said, the NiCd
cells have a "memory" problem, and the only
way to "reset" that is to do an almost complete discharge and then charge;
sometimes this is needed moer than once for recovery.

I "resurrected" a NiCd pack in a wireless phone once - it wasn't holding
a charge, like I'd get two minutes of talk time, it'd beep, and go dead.
Really pissed off one of my clients when the phone went dead on him.

So I took the battery out, poked a 1K resistor into the connector, and
let it discharge to approx. 0. Stuck it back in the phone, let it charge
for a day, and it worked like new.

I don't recommend this unless you're prepared to spring for a new
battery if you actually kill it.

Good Luck!
Rich

 

[ehsjr]

Not true. NiCds and NiMH batteries can be fully discharged, but not below 0V
on any cell. A multi-cell NiCd battery may reverse charge a weak cell which
*will* kill it. NiCds should be stored discharged (but self-discharge is good
too).

OTOH, lead-acid batteries must never be fully discharged. Deep discharging
them tends to warp the plates causing shorts. "Marine" batteries have thicker
plates (thus lower power-density and higher internal resistance) and are less
susceptible to plate warping.




The "memory" problem isn't. It's much legend about a totally different issue
(one that has been pretty much non-existent for 20 years).




Over-charging and reverse charge during discharge are by far the most common
cause of early failure of NiCds.




Not less than 80% of rating? Nonsense. Lead-acids shouldn't be discharged
below 20%, perhaps. NiCds can be run to down to zero as long as the cells
don't reverse polarity.

Not a pack, just an individual cell. The *proper* discharge
level - the level at which the cells should be considered
completely discharged - is about .9v per cell. With a single
cell there is no risk of cell reversal, but with a pack,
discharge should be limited to that .9v per cell level.

Lead-acid 12V wet cell batteries should never be discharged
below 10.5 volts.

Ed

 

[Keith Williams]

Not a pack, just an individual cell. The *proper* discharge
level - the level at which the cells should be considered
completely discharged - is about .9v per cell. With a single
cell there is no risk of cell reversal, but with a pack,
discharge should be limited to that .9v per cell level.

No, that's the "proper" voltage for a multi-cell application. A
single NiCd cell can "properly" be discharged down to 0V. There
isn't much charge under .8V or so though. Reverse charge is the
worry here (which cannot happen with a single cell).

Lead-acid 12V wet cell batteries should never be discharged
below 10.5 volts.

That depends on the design. "Deep cycle" or "marine" batteries are
better at this than "starter" batteries because of their mechanical
construction.

 

[John Woodgate]

I read in sci.electronics.design that Keith Williams <[email protected]>

That depends on the design. "Deep cycle" or "marine" batteries are
better at this than "starter" batteries because of their mechanical
construction.

The electrolyte concentration is different as well.

 

[ehsjr]

No, that's the "proper" voltage for a multi-cell application.

You are agreeing with what I wrote. Why the word "No" at the
start of your sentence?

A single NiCd cell can "properly" be discharged down to 0V.

That's what I said. "Not a pack, just an individual cell"
which refers to your statement "NiCds can be run down to
zero..."

There

isn't much charge under .8V or so though. Reverse charge is the
worry here (which cannot happen with a single cell).

That's what I said. "With a single cell there is no risk of
reversal, but with a pack, discharge should be limited to
that .9V per cell level."

That depends on the design.

No - finally we disagree! Regardless of design, discharging
a wet cell 12V battery below 10.5 is a no-no. That includes
deep-cycle/marine batteries. The open circuit voltage swing
from 100% charged to 100% discharged is only about 2 volts.
http://www.windsun.com/Batteries/Battery_FAQ.htm
These batteries are 100% discharged when they reach 1.75
volts per cell (10.5 across the battery), per the site above.
Exide specifies a higher voltage: their FAQ says the battery is
100% discharged at 11.7 volts
http://www.exideworld.com/faq/faq_marine.html#stateofcharge

This site lists ~11.8 volts as 100% discharged:
http://www.uuhome.de/william.darden/carfaq4.htm#measure

This site shows 11.5 volts as 100% discharged:
http://www.mpoweruk.com/soc.htm

Even if you do not go below 10.5 volts, removing most
or all of the charge (and by that I mean I mean lowering
the state of charge such that the battery voltage approaches
10.5 volts) reduces the battery life. For exmple, one
of the sites mentions indicates that you'll get more than
double the number of charge-discharge cycles from a deep
cycle battery if you keep the discharge level to no more
than 50% than if you keep it to no more than 80%.

Ed

 

[Phil Allison]

"ehsjr"

Not a pack, just an individual cell. The *proper* discharge
level - the level at which the cells should be considered
completely discharged - is about .9v per cell. With a single
cell there is no risk of cell reversal, but with a pack,
discharge should be limited to that .9v per cell level.

** A requirement that is practically impossible to comply with for packs of
more than about 4 cells.

Eg. A a 6 cell ( nominal 7.2 volt) Ni-Cd pack where all cells are
identical.

Freshly charged = 9.0 volts.

On load = 7.5 volts ( at half capacity)

End point = 6.0 volts.

Load cut off = 5.4 volts ( using the 0.9 volt per cell criterion )


However -

In the real world, one cell will always be weakest, reach end point first
then go very rapidly to zero.

The pack will still deliver 5 x 1.25 = 6.25 volts with one cell at 0
volts.

So, the weakling can be reversed to -0. 85 volts before the 5.4 volt load
cut out operates.

With more than 6 cells, the situation gets worse.




........ Phil

 

[ehsjr]

"ehsjr"





** A requirement that is practically impossible to comply with for packs of
more than about 4 cells.

Eg. A a 6 cell ( nominal 7.2 volt) Ni-Cd pack where all cells are
identical.

Freshly charged = 9.0 volts.

On load = 7.5 volts ( at half capacity)

End point = 6.0 volts.

Load cut off = 5.4 volts ( using the 0.9 volt per cell criterion )


However -

In the real world, one cell will always be weakest, reach end point first
then go very rapidly to zero.

Yup. When the pack ages to the point where one of the batteries
is weak enough for the described scenario to occur, it is time
to replace or repair it - or live with shorter times between
recharge/lower power.

Ed

 

[Phil Allison]

"ehsjr"

Yup. When the pack ages to the point where one of the batteries
is weak enough for the described scenario to occur,

** That is NOT what I wrote and not what was being demonstrated.

Clearly you don't want to know the facts.




............ Phil.