The "battery" light has nothing to do with the condition of the battery. It means the generator is not recharging it as you drive. The resulting low system voltage will confuse the many computers on the car and make them do weird things or turn off. That's when those computers turn on their warning lights.
You will need to charge the battery at a slow rate for at least an hour, then it will give you from a half hour to an hour of driving time before it runs down again. That time will vary depending on how much you use the head lights, how often the radiator fan runs if you're in stop-and-go traffic, how fast you run the heater fan, etc.
When you try to get the engine started with jumper cables, if your battery is seriously run down, it will take from five to fifteen minutes before it STARTS to take a charge. That's why even if you get the engine started, it won't stay running. The battery is still dead and unable to power the electrical system.
It's the generator and charging system that needs to be tested. There's multiple ways the generator can fail. Not all failures turn on the "battery" light. When they don't turn it on, it means the generator is still producing a little current, but it's not enough to meet the demands of the entire electrical system under all conditions. Your mechanic will check the system for "full-load output", regulation voltage, and "ripple" voltage.
Sunday, October 6th, 2013 AT 12:39 PM