Testing a Battery

[RF5BPilot]

I have a vehicle with a battery that is less than a year old. A few days ago, I accidentally left a circuit on and the battery slowly ran down to flat dead over night. (Even though it was a small draw, it's a small battery.) The battery is a traditional, flooded cell, removeable cap (i.e., put in distilled water) battery. I put on a slow charger that, over the past couple of days, should have fully charged the battery.

The short question is, should I trust it now? Is there a cell that has gone bad? (I realize that this probably shortened its overall life....but I'm more interested in its current health.)

Possible tests include: checking output voltage & specific gravity of the fluid from each cell.

Any recommendations about testing to assess whether I should get a new one?

Thanks.

[Popolou]

Actually, testing a bettery is best done when its under load. It might show up as a full 12v when you hook a multimeter across it, but if a bettery has already suffered, it might fail under the moment you crank the motor.

You may be able to take it to a shop where they have equipement to do this because it could start to become somewhat precarious.

Regards

Popolou

Edited September 6, 2007 by Popolou

[Tool Pants]

Just about any auto parts place has a battery tester. Fully charge the battery then have them do a load test.

[RF5BPilot]

I guess removing it wouldn't be too hard. I was just thinking narrowly that I didn't have a tester that I could use to apply a load. Will see what places are nearby that might test it.

I may get an indication of major problems when I first crank it over. Also, I suppose, if there's a short, the battery charger may not go into "float" mode and just keep charging.

[1999Porsche911]

Just leave the key on, turn on the headlights for 30 minutes and then try to start. If it starts fine, your battery is in good shape.

[demosan]

I guess removing it wouldn't be too hard. I was just thinking narrowly that I didn't have a tester that I could use to apply a load. Will see what places are nearby that might test it.

I may get an indication of major problems when I first crank it over. Also, I suppose, if there's a short, the battery charger may not go into "float" mode and just keep charging.

RFSB,

Yo ucan get the battery load tested wit hit in the car. At the same time they can check your alternator to ensure it is up to snuf as well. Sears is one source that I believe offers this as a freebie!! Good luck!!

Demosan

[fastboydave]

Yeah, agree with a couple of the guys here. Fully charge it, wack on ALL loads (especially lights, heated rear screen, PCM, aircon etc) basically as much load as you can, leave it a couple of mins and crank to start. It will sound 'slower' but should crank it over and start. Alternatively, get it tested by a battery place, quick and easy to do.

I dont think you will have killed the battery, what kills the battery is more the charging after you have run it flat, rather than the running flat. As you 'trickled' it, you have done the best you can. This is beacuse the intially surge of current into a completely flat battery distorts/ruins the plates. Therefore over the course of time eventually the plates are shot and you get a build up of crystals which take away the capacity of the cells (or something like that).

[RF5BPilot]

Thanks all.

I checked it last night. The slow charger had been on several days and was in "float" mode, meaning there wasn't a significant short drawing power. The charger isn't strong enough to really make the battery hot, so didn't attribute anything to the battery being cool. With lights and radios on, it fired right up. While running, the amp meter seemed to have pretty normal readings. Later in poor weather I will probably take the battery out and have it tested. Will need to make sure whoever does it has a tester that can adjust to a smaller battery (about the size of a large garden tractor battery rather than a 500+ amp typical auto battery).

I do keep a solar panel on it for trickle charging when it's not used....but if there's a real problem, I doubt it would keep up with a serious internal drain. So, my best guess is that (especially since tha battery was pretty new and has been kept well charged) -- it is ok for the time being.