My '97 Poniac Bonnieville's battery went out but the lights still work what could be the problem?
Tuesday, November 23rd, 2010 AT 12:40 PM
What's the symptom? If the lights are normal brightness, the battery is fine. You can prove that by measuring the voltage between the two terminals with an inexpensive digital voltmeter. A fully charged battery will measure near 12.6 volts. A good but discharged battery will read around 12.0 volts. A battery with one shorted cell will read close to 11.0 volts.
It is WAY more common on GM cars to have a defective generator. If the engine will start and run with a jump start, after removing the jumper cables, measure the battery voltage again. While running, you must find between 13.75 and 14.75 volts. If it is low, suspect a defective generator. It is common to go through four to six of them in the life of the car. (This only pertains to GM products). Many professionals are finding that to reduce repeat failures, replace the perfectly good battery at the same time. The old battery will work fine in older cars from before 1987, but in the newer models, the generators have a big tendency to develop harmful voltage spikes. As batteries age, they lose their ability to absorb and dampen those spikes.