Keeping a 12v battery charged above 80%

[W. eWatson]

I had a fellow out to do some electrical work that involves one 12v
marine battery. The battery will be used about 4-6 hours a night
sporadically. Maybe 15-20% of the time. He offered that it should be
recharged every day, and keeping it above 80% was important for the life
of the battery. Somehow that seems a bit high. Apparently, there's a
charger of some sort that costs about $150 that will adhere to that
schedule. Comments?

 

[Wrecker]

I had a fellow out to do some electrical work that involves one 12v
marine battery. The battery will be used about 4-6 hours a night
sporadically. Maybe 15-20% of the time. He offered that it should be
recharged every day, and keeping it above 80% was important for the life
of the battery. Somehow that seems a bit high. Apparently, there's a
charger of some sort that costs about $150 that will adhere to that
schedule. Comments?

I bought a Battery Tender Jr. for my motorcycle. A
microprocessor-controlled marvel that usually did nothing at all, but
sometimes it drained my battery below the level that it started at.
Never once did it charge the battery. The "Lifetime" warranty required
me to ship it back to Florida for repair, along with handling fees,
diagnostic fees, return shipping fees, etc. that approached the retail
cost of the charger. After a year, I smashed it with a sledgehammer and
threw it in the trash.

 

[W. eWatson]

I bought a Battery Tender Jr. for my motorcycle. A
microprocessor-controlled marvel that usually did nothing at all, but
sometimes it drained my battery below the level that it started at.
Never once did it charge the battery. The "Lifetime" warranty required
me to ship it back to Florida for repair, along with handling fees,
diagnostic fees, return shipping fees, etc. that approached the retail
cost of the charger. After a year, I smashed it with a sledgehammer and
threw it in the trash.

I can certainly sympathize with that. I've had a few instances where I
thought I might bring some faulty equipment into a mfger's office and
drop it on the floor.

 

[Jasen Betts]

I had a fellow out to do some electrical work that involves one 12v
marine battery. The battery will be used about 4-6 hours a night
sporadically. Maybe 15-20% of the time. He offered that it should be
recharged every day, and keeping it above 80% was important for the life
of the battery. Somehow that seems a bit high. Apparently, there's a
charger of some sort that costs about $150 that will adhere to that
schedule. Comments?

I own a cheap 4A Arlec charger with electronic control (electronic
control comprises a pcb with a pair of SCRs, a transistor, a zener
diode, and some resistors)

It charges to about 14V gradually reducing the charge rate.
that would be stages 1 and 2 of the diagram here.

http://batteryuniversity.com/learn/article/charging_the_lead_acid_battery

I use it for charging accidentally discharged car batteries, and
for charging the sealed lead acid battery in childs electric trike.
(it charges this smaller battery at 1A gradually tapering off)

It sounds like you'd want one that also does stage 3 "float charge" for your
application. $150 does sound quite expensive (about twice what I would
expect) but I don't know of a more competively priced off-the-shelf
solution.

 

[[email protected]]

I had a fellow out to do some electrical work that involves one 12v
marine battery. The battery will be used about 4-6 hours a night
sporadically. Maybe 15-20% of the time. He offered that it should be
recharged every day, and keeping it above 80% was important for the life
of the battery. Somehow that seems a bit high. Apparently, there's a
charger of some sort that costs about $150 that will adhere to that
schedule. Comments?

Black and Decker used to have a selectable 1 and 2 amp charger. It
turned off when the battery was fully charged. I've been using one of
them for a number of years to keep the grandkids' battery-powered
vehicles charged (beats using the "battery burner" that comes with the
vehicles). The charger was about $30. I think they still have a
similar one that only has the 2 amp output. That would be OK foryour
application, but the small SLA batteries in the kiddie cars live
longer if the charge is limited to 1 amp.

Ideally, a lead acid battery is never discharged below 50% - that's
the standard used in designing the battery system for solar or other
alternate energy. The less a lead acid battery is discharged, the
longer it lasts - the electrochemical reactions (charge/discharge) are
reversible, but there is a limit.

 

[Bob Engelhardt]

...
Ideally, a lead acid battery is never discharged below 50% - ...

How is charge measured? Voltage? Does 50% mean a 12v battery at 6v?
That doesn't sound right.

 

[Sjouke Burry]

How is charge measured? Voltage? Does 50% mean a 12v battery at 6v?
That doesn't sound right.

That is because the talk was about the charge, not the voltage.
8-10 volt means almost empty.
Below that you are trying to kill the battery.

 

[Winston]

That is because the talk was about the charge, not the voltage. 8-10
volt means almost empty.
Below that you are trying to kill the battery.

Below 12v you are trying to kill the battery.
http://batteryuniversity.com/learn/how_to_measure_state_of_charge

--Winston

 

[[email protected]]

How is charge measured? Voltage? Does 50% mean a 12v battery at 6v?
That doesn't sound right.

Integrate the current taken out of a fully charged battery (integral of
current is charge). When that number reaches ~50% of the rated capacity,
stop.

 

[Bob Engelhardt]

That is because the talk was about the charge, not the voltage.

....

I know. That's why I asked: "How is charge measured?"

 

[Bob Engelhardt]

...
http://batteryuniversity.com/learn/how_to_measure_state_of_charge

More specifically:
http://batteryuniversity.com/learn/article/how_to_measure_state_of_charge

Which says basically that charge is pretty hard to measure. I.e., there
isn't a simple, accurate technique.

 

[Bob Engelhardt]

Integrate the current taken out of a fully charged battery (integral of
current is charge). When that number reaches ~50% of the rated capacity,
stop.

batteryuniversity calls that coulomb counting. Even that is subject to
the battery actually having its rated capacity when it's fully charged.

 

[Winston]

More specifically:
http://batteryuniversity.com/learn/article/

how_to_measure_state_of_charge

Quite right. Thanks!

Which says basically that charge is pretty hard to measure. I.e., there
isn't a simple, accurate technique.

'Same is true for anything else we measure, for very demanding
levels of accuracy. However, one can also take the article
to say that measuring open-circuit terminal voltage (after
allowing the battery to rest) yields accuracy that is quite
acceptable for just about anything a hobbyist is likely to do.

Yes? No?

My nice torque wrench serves perfectly fine to be within +-5%
of the *real* reading. I don't have a need to know my lug
nut torque with much better accuracy than that.
'Same is true for my ammeters. I know that there is a burden
voltage on top of calibration errors and the relative sloppiness
of all physical things, but I accept their readings if I am
comfortable that the reading that I see is likely to be
'close enough'. (Yes, rarely I *am* fooled by readings that
are not nearly 'close enough').

Why take away these tools (and hundreds of others) as being
'too imprecise' if great accuracy is not required?


--Winston

 

[[email protected]]

batteryuniversity calls that coulomb counting.

Well, the unit of charge is the Coulomb, so that makes some sense. ;-)

Even that is subject to
the battery actually having its rated capacity when it's fully charged.

If the battery is so bad that 50% isn't enough margin of error, it's done
anyway. A battery is considered "bad" if its capacity is 80% of that of a new
battery.

 

[tuinkabouter]

How is charge measured? Voltage? Does 50% mean a 12v battery at 6v? That
doesn't sound right.

Read the wiki: https://en.wikipedia.org/wiki/Lead–acid_battery
Look at the open voltage caracteristic (the name is misleding):

https://en.wikipedia.org/wiki/File:Lead-acid_voltage_vs_SOC.PNG

When a lead battery starts gassing it is full.

 

[amdx]

I bought a Battery Tender Jr. for my motorcycle. A
microprocessor-controlled marvel that usually did nothing at all, but
sometimes it drained my battery below the level that it started at.
Never once did it charge the battery. The "Lifetime" warranty required
me to ship it back to Florida for repair, along with handling fees,
diagnostic fees, return shipping fees, etc. that approached the retail
cost of the charger. After a year, I smashed it with a sledgehammer and
threw it in the trash.

I note Amazon.com has 761 customer reviews.
95% are 4 or 5 star and 84% are 5 star.
Leaving only *5% unhappy with the product,
looks like you got a bad one.

* I think it might be lower, as unhappy people
are more likely to complain.

Mikek

 

[Wrecker]

On 6/9/2012 10:57 PM, Wrecker wrote:

I note Amazon.com has 761 customer reviews.
95% are 4 or 5 star and 84% are 5 star.
Leaving only *5% unhappy with the product,
looks like you got a bad one.

Yep. And when I needed the warranty (5 years I think it was, not
lifetime), I found it was laughable.

* I think it might be lower, as unhappy people
are more likely to complain.

People also like to push their choices, and rally others to follow.
Everyone likes to be an authority. I see that so often on hokey
Newegg.com reviews.

 

[amdx]

Yep. And when I needed the warranty (5 years I think it was, not
lifetime), I found it was laughable.


People also like to push their choices, and rally others to follow.
Everyone likes to be an authority. I see that so often on hokey
Newegg.com reviews.

hmm.. maybe!
I bought an FM transmitter from Amazon 6 months ago and wrote a positive
review after setting it up and seeing how great it worked. Just this
morning I was thinking how well it works and I should write another
review and tell everyone!
http://www.amazon.com/0-5-Fail-Safe...339624789&sr=1-12&keywords=fm+transmitter++++
Dang, now I'm not happy the price has dropped 50%!
Ok, I'm still happy, I might but another one.
Mikek

 

[[email protected]]

hmm.. maybe!
I bought an FM transmitter from Amazon 6 months ago and wrote a positive
review after setting it up and seeing how great it worked. Just this
morning I was thinking how well it works and I should write another
review and tell everyone!
http://www.amazon.com/0-5-Fail-Safe...339624789&sr=1-12&keywords=fm+transmitter++++
Dang, now I'm not happy the price has dropped 50%!
Ok, I'm still happy, I might but another one.
Mikek

Wrecker makes a good point. I see tons of reviews where the buyer just
unwrapped the present and talks about how well it works. OTOH, I generally
look at the negative reviews. I want to see what problems were encountered
and how they were fixed. If the seller takes care of the problem, that's a
positive in my book.

 

[Grant]

Read the wiki: https://en.wikipedia.org/wiki/Lead–acid_battery
Look at the open voltage caracteristic (the name is misleding):

https://en.wikipedia.org/wiki/File:Lead-acid_voltage_vs_SOC.PNG

When a lead battery starts gassing it is full.

No, when a LA battery starts gassing it is about 80% charged, putting
in that last 20% take three hours at C/10, after up to five hours at
C/5 to get to the gassing point.

Old numbers for flooded traction batteries. Sealed LA batteries may
have a different charge curve.

Grant.