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Dear Jim,

My 1993 Plymouth Laser (L4, 1.8 L) is having an electrical problem I can't figure out. In the daytime, I can drive all around, then let the car sit overnight and it starts just fine the next morning. Whenever I drive for a while at night, however, the battery will usually be dead in the morning.

If I jump-start, the car runs fine until the next time the battery dies.

How does the battery know what time of day it is, Jim, and what can I do about this?

-- Cyndi Wakefield

What you're experiencing may sound strange, sister, but I assure you that nothing under the hood of your Laser knows what time it is.

That said, it's not really the battery that's giving you trouble here. It's a bad alternator that's not cranking out the full 13.2 volts it should.

Think of the battery as the car's primary energy source and the alternator as a charger that supplies extra current when you need it. If either of them isn't working right, your car will have problems with its starting and charging systems.

I'll bet that, with the cooler temperatures these days, you're not using the air conditioning.

During the day, the battery isn't being used for many tasks, so there's not a very heavy load on the electrical system. As a result, your weak alternator is able to keep the battery charged.

At night, you have your lights on and, when it's chilly out, maybe the heater too. The alternator gets overwhelmed, it can't keep up and your battery slowly loses its charge.

Have that alternator tested at the shop. No one really repairs these things anymore, so you're going to need a new unit for probably around $100 plus labor.

The whole job shouldn't run more than $200, but after it's done, sister, you'll get back that peace of mind that comes from knowing you can start up whenever you need to.

Tip of the Week:

It's a good idea to get that alternator checked at least once a year, drivers; especially if you're noticing things such as sluggish power windows, dim interior lights or bulbs burning out faster than usual. Any of this can mean trouble with the alternator or the voltage regulator that's housed inside it.

If you know the battery is good and you're still seeing symptoms such as these, get that charging system checked.

Buffalo Jim, owner of Allstate Auto & Marine Repair in Las Vegas, writes a weekly column. Send your automotive questions to him at buffalojim@lasvegasniftynickel.com. If Jim picks your question to answer in Nuts & Bolts, you'll also be the proud recipient of a deck of official Buffalo Jim playing cards, presented in a classy, tin box bearing his hairy image.