# How much permanent damage did I do to my car battery?

Discussion in 'Electronic Basics' started by AC/DCdude17, Jul 2, 2003.

1. ### AC/DCdude17Guest

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One of the door was ajar on my car and a small light got left on. I
haven't driven since Monday afternoon, so it's been on for good 48
hours. When I tried to start it, no nothing. Not even a click. The
battery was completely drained.

The battery is on charger right now and I'll put it back in after it's
fully charged, but how much permanent damage might I have done to the
battery? It's an Everstart brand from Wal-Mart.

2. ### John PopelishGuest

I would make a swag that you have killed 5% to 10% of the batteries
capacity by this full discharge/charge cycle.

3. ### AC/DCdude17Guest

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All I have is a Exide 6A dumb charger that's not electronically controlled.
I will terminate the charge when I hit 14.5 to 15V. Does that sound ok?

4. ### Kevin McMurtrieGuest

Hold it at 14.4 - 14.6 volts for about 6 hours if you can. Driving the
car will apply the same voltage. Don't let it go higher for very long.

5. ### AC/DCdude17Guest

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Ok, the battery is 525CCA and I'm guessing 75 RC and it's still drawing 4A
even though the voltage is up to 15A. In my experience, typical auto
battery goes down below 2A when it's done charging and shows "full" on the
needle meter on the charger.

If this is abnormal, what would cause charge current to not drop down
properly?

I have pumped in total of 1.08kWh into the charger, so I'm guessing about
800 to 850Wh went to the battery. Shouldn't be too much to damage a totally
drained battery, right?

6. ### BrowntimdcGuest

Periodically holding 15V+ for a short time (a couple of hours) will
actually help a car battery. It's called equalizing. I equalize my car
battery once a month during the winter.

"The Equalizing Charge
After several months, the individual cells that make up the battery may
differ in their states of charge. Voltage differences grater than 0.05
volts between the cells indicate it is time to equalize the state of charge
of the individual cells. In order to do this, the battery is given an
equalizing charge. An equalizing charge is a controlled overcharge of an
already full battery. Simply continue the charging process at the C/20 rate
for 7 hours after the battery is full. Batteries should be equalized every
5 cycles or every 3 months, whichever comes first. Equalization is the best
way to increase deep cycle lead-acid battery life.Battery voltage during
the equalizing charge may go as high as 16.5 volts. This is too high for
many 12 volt electronic appliances. Be sure to turn off all voltage
sensitive gear while running an equalizing charge."

Trojan batteries calls for 15.5V equalizing:
http://www.taosgreensolar.com/pdf_folder/battery_maint.pdf

EcoElectric Corporation recommends 15.2V:
http://www.ece.drexel.edu/sundragon/tech/batt.test.part1.html

More:
http://www.exomarine.com/products/NZ1008/library/whitepapers/whitepaper_cru
zpro_marine_battery_care.asp

Tim

7. ### Mike RingGuest

Ouch.

http://www.uuhome.de/william.darden/

Mike R

8. ### Henry KolesnikGuest

Car batteries are not designed for very many total discharges like deep
cycle batteries that are used for trolling motors on boats...
From what I recall you can totally discharge an auto battery xteen times and
that's it..
So you lost somewhere between 5 and 15%...
If your trickle charger isn't sophisticated, charge for a couple of hours,
enough to start the car and let your car's alternator take car of it..
If the battery fails, use the warranty..
good luck
hank wd5jfr

9. ### AC/DCdude17Guest

X-No-Archive: Yes

The battery was drained to 0% capacity for sure. I read somewhere that
Ah capacity is about 60% that of RC and that comes to about 45Ah. I
metered the energy going into the charger and I pumped in 1.1kWh. Give
85% for charger efficiency and 80% charging efficiency, it comes to
about 0.748kWh useful charge and I'm guessing the battery's capacity to
be ~0.54kWh.

Anyways I put it back in the car and followed one of the testing
procedure. I disabled the fuel injection by flooring the pedal(since I
didn't want to unhook things on ignition) and cranked the starter for
15sec. Had my DMM hooked up to the battery in minimum voltage latch
mode and it never went below 10.9V. Looks like I pass.

It doesn't get terribly cold in the Pacific NW so I don't think I should
be worried.