That's not a common question but the battery's capacity goes down as it ages and some of the lead flakes off the plates so it's easier to think about the percentage of its capacity that is used. As the battery nears the end of its expected life, you can use possibly 20 percent of its capacity to start the engine but what remains of the battery will also recharge very quickly.
The starter for a small engine will draw around 100 amps for just a few seconds. A pair of head lights will draw close to 10 amps. Many years ago a new battery could run those head lights for about two hours and still start the engine. A battery that was almost at the end of its life might only run those head lights for 15 minutes but it could still be good enough to start the engine if too much cranking time wasn't needed. Batteries today are quite a bit better.
I know I'm kind of rambling because this is not a normal question. Is there a problem you're trying to solve that can put the information in better context?
Friday, August 3rd, 2012 AT 7:08 AM