Charging battery, how many amps is too much?

[bandhawk]

Did a search and didn't really find an answer...

I have an Interstate Megatron battery, 750 CCA/900 CA.

I have a Wal-Mart charger which has options to charge at Amps of 2, 10, 20, or 40. I know a 2 amp trickle is nice to keep the battery charged, but is using the 40 amp setting too ambitious for recharging my dead battery? Will it hurt my battery or cause a bunch of electrolyte boil-over? Currently I'm using 20 amps...I feel like it's middle of the road.

[HawgRyder]

Batteries are also rated with Amp/Hour numbers.
This means you can pull so many amps for an hour or half that many for 2 hours etc.
To charge a battery without damage, the accepted level is 10% of the Amp/Hour rating.
This to recharge a dead or almost dead battery.
Bs advised...never completely kill a battery if you can help it.
It does nasty things to some...and they may not recover even if correctly charged.
Bob

[911pcars]

Generally speaking, the charge limit depends on the amount of heat generated. "Excess" heat can distort the plates and shorten battery life. You can go to the many "battery charging" sites on the net and get the exact numbers. I'd say 20 amps is a little ambitious for maintaining a battery; 1-2 amps should be fine as long as the charger shuts down once it's fully charged. Even when the battery is fully discharged, use a low charging current. This brings the battery up to charge slowly and w/o overheating. A 24 hour charge should be long enough to tell if the battery is okay.

Sherwood
http://members.rennlist.org/911pcars

[bandhawk]

bob, sherwood...thanks for the advice

[scottb]

Originally posted by bandhawk
I have a Wal-Mart charger which has options to charge at Amps of 2, 10, 20, or 40.

That's a serious charger. What's the make and model number?

Thanks.

[RickM]

Charlie,
This is what I know from past experience with batteries (Interstate as well).... If the battery was dead I'd do a 10 amp charge overnight. If it didn't crank the engine over in the morning chances are the battery is shot. I'd use 40-50 amps for 1-5 minutes to jump start. As mentioned 2 amps (or lower) is ideal for a maintenance charge. However, I would (and do) use an intelligent trickle charger like the "Battery Tender" or others as they monitor voltage and current and adjust accordingly to prevent boil over, overcharging and in some cases build-up on the plates(through pulsing).

[911pcars]

Just to add; don't rely on the alternator to recharge the battery. Porsche alternators don't seem to like creating large amounts of current (shortens their life). If the battery is discharged, use an outside charger to bring it up to spec before running the engine.

Sherwood

[bandhawk]

scottb: it's a Vector "Smart Automatic Battery Charger". Model # VEC1093A...Wal-Mart Special. It also has a 100 amp mode to jump the car, too. But I haven't used 100 yet.

911pcars: Yeah, I've seen the other threads involving alternator trouble. I'm making sure mine has a full charge before I drive again.

[Miguel Antonett]

Is it correct to disconnect the negative terminal when recharging the battery in the car? In such way the charging current doesn't go through the system/alternator, or it doesn't make any difference???

[911pcars]

Not really necessary with small amperage chargers. For heavier charging rates, disconnect the ground (neg.) cable.

Caution. Disconnect before charging. Don't do this while the battery is charging. Charging vapors are explosive and can cause a kaboom noise (and EFX) if any sparks are created nearby.

Sherwood