Q I have a 2003 BMW Z4. The battery died twice without warning because of old age. I've been advised to check the battery regularly, especially after one year. I bought a $50 battery tester so I can check it myself every other week. Is this is a good plan in terms of battery reliability?

A I admire your willingness to test the battery on a regular basis, but how is testing the battery going to prolong its life? It's not, but it may give you an idea of when the battery is starting to fail.

Battery life is somewhat unpredictable. Most automotive batteries seem to survive three to five years -- nicely in line with their warranties. I don't think a car owner can extend the life of a battery, but I do believe a car owner can shorten a battery's life.

The major factors in battery life seem to be environmental/ambient temperatures, state of charge, level of electrolyte, quality of terminal connections and security of battery mount. Car owners can't keep it from getting cold outside, but they can influence the other factors.

If you absolutely do not want to deal with a dead battery, there's a relatively simple answer: Replace the battery every two or three years. Is this potentially wasteful? Yes, but unless you accidentally discharge the battery by leaving the lights on or something similar, the car will always start.

Q My 1998 Grand Marquis has 117,000 miles on it, and it runs like the day I drove it out of the dealership, with one exception. Since about 105,000 miles, the alternator light will come on and off at irregular times. I have a voltmeter I plug into the cigarette lighter, and with the car off it reads 12.1 volts; while running the car during the day it reads 13.8 to 14.1. At night when the lights are on, it reads 13.3 to 13.4. At night the battery light comes on and off more often.

The shop could not help because, of course, the light was off. Any suggestions would be appreciated. My guess is the voltage regulator inside the alternator, but I hate to spend the money for a new alternator and still have the same problem.

A See above: Install a new battery. A fully charged automotive battery at room temperature should develop 12.6 volts, give or take a tenth or two. Double-check the battery voltage at the battery itself with a digital voltmeter. If it confirms the 12.1-volt reading, the battery is weak. I suspect you'll see a bit more voltage at the battery, but if it's not above 12.3, the battery is suspect.

You can have both the battery and alternator load tested to confirm their performance, but the voltage readings you see with the engine running indicate that the alternator is performing normally.

Q I need to purchase a new battery charger. I want one that will charge batteries across the board -- motorcycles, cars, etc. Some have a 50-amp starting feature, but someone told me that 50 amps isn't enough to start a car. Right or wrong?

A Most of my collection of battery chargers have come from garage sales. Some are 6/12 volt, most are in the 6-to-10 amp charge range and fully automatic, one is just a "float" or maintenance charger, and one has the 50-amp boost.

Buy an inexpensive battery maintainer to keep infrequently used batteries properly charged, and buy a 2/10/50 automatic charger. While 50 amps may not start the car, that level will recharge the car's battery quickly and provide a boost to crank the engine.