Battery choices

[Jaxonalden]

Originally Posted by JackG

A small correction... the battery is used to start the car. Once running, the alternator supplies *all* the current to run the car, and it also recharges the battery. The battery is simply a storage device used for starting and for supplying power when the alternator isn't spooled up.

Having a smaller battery will not put a bigger strain on the alternator. After all, it still takes the same amount of energy to start the car, so the alternator has to replace the same amount of energy back in the battery after the start. And it's already sized to handle all those electrical items you listed.

If you add big amps for your stereo, and you run them at loud, thumping levels all the time, you may exceed the alternator's output capability. The fix there is to upgrade the alternator. A bigger battery is a patch at best. If you're exceeding the alternator's output capability on a nearly constant basis, the battery will eventually be drained, but that's an extreme case.

Jack,

I totally disagree with everything you wrote and stand behind my thread. The car does not run off of the alternator, it pulls power from the battery. The battery is a constant, large capacity source of ~12 volts of electricity. The alternator does nothing more than recharge the battery at 13.5-14.5v. Anything less than 13.5v and the battery will not recharge ("Alt" idiot light). The alternator produces A/C power thats converted to D/C through diodes and the voltage regulator does just that, it regulates the flow of current to the battery. Flow starts when battery volts fall below 13.5v and shuts it off at 14.5v.

So as I said;

"It's all about electrical capacity. Don't forget your putting a strain on the alternator trying to keep up...if you have a small battery." That's because the alternator is not meant to constantly supply power and will eventually heat up (which is the limiting factor) and fail.