Dead battery

Q: Greg, my Lexus has a battery that goes dead when I don’t use the car for several weeks. My dealer tells me it is because there is a draw on the battery even when the car is off, and it’s common with the new computer-controlled engines. Is he right? Also, why can some batteries go dead and when they sit, they come back to life? — Michael G., North Carolina

A: Michael, your Lexus dealer is correct. Even when your car is turned off, there is a draw on your battery to keep the computer memory up to date and things like your car’s clock running properly. I had the same problem when I would let my ‘94 Trans Am sit for three or four weeks between starts. I bought a trickle charger (available at all auto stores), and that corrected my problem.

As for why some batteries go dead and then “come back to life,” www.howstuffworks.com explains it best: The “self-recharging” feature of batteries is most noticeable in a car battery. In some cases, you can crank the engine until the battery seems totally dead, then come back an hour later and crank it again. The higher the drain on the battery (a car’s starter motor is an incredibly high-drain device!), the greater the effect.

In any battery, be it an alkaline battery found in a flashlight or a lead acid battery in a car, reaction products like hydrogen gas build up around the two poles of the battery and slow down the reaction; eventually the battery begins to look “dead.” If you let the battery rest for a while, the hydrogen gas dissipates and the battery “comes back to life.”