Does draining a car battery reduce its lifespan? If so, how??

Question

Ok, I understand that a car battery -- any battery -- has a finite lifespan; you cannot create energy indefinitely from a fixed batch of chemicals. In the normal course of operating a car, the battery is recharged as it goes, and it has an expected life of, say, 5-8 years.

But does leaving your lights on and car off, for instance, reduce the lifespan of the battery? Once it's been drained, why doesn't recharging it (by a jumpstart and the car's alternator) just simply refresh it as a car's normal operation would?

What's the difference between the two processes that reduces the battery's life in one case but not the other? What's happening at the chemical-reaction or molecular level?...

Thanks.

Answer 1

Everytime you discharge a car battery you can never charge it up to the level it was before the discharge. If you could, your battery would never die. Nothing is 100% efficient. So leaving your lights on, or any deep discharge where the battery is completely drained would take a lot out of the battery, and when it recharges, you have a difficult time getting it way up to the point before if discharged. Lights drain the battery very slowly, so you wouldn't take too much out of the lead and lead sulfate and oxide electrodes unless the voltage was allowed to drop very low. Quick discharges like turning the starter with 200 amps is quite a drain, and has an affect on the electrode plates similar to what it has undergone during a deep, slow and steady drain rate. Sort of like recharging you if you walked a mile or if you sprinted 500 yds. The difference is time, but pretty much the same amount of energy is lost when you can't go any more.

You are using up water, H2SO4 and electrode materials during the charge and discharge, and there are deposits that grow on the plates over time making them less efficient everytime you go through a cycle.

Answer 2

Batteries work basically by sucking ions off of one metal, then passing them onto another.

Some batteries are designed or have a chemistry that allows them to prefer to be deeply drained before being refilled. Snowmobile batteries, NiCad batteries, etc. all like being used a lot before being recharged.

Other designs and chemistries prefer being as charged as possible- car batteries, Lithium Ion, etc.

Try http://www.batteryuniversity.com for more info on this subject.

Answer 3

Regular car batteries shouldn't be deep discharged, use a marine battery for that.