Three weeks is the maximum a car can sit and still be expected to start due to the memory circuits on all the computers draining the battery. It takes 20 - 60 minutes with a battery charger just to make the battery acid conductive before it will start to take a charge; then it could take two hours to fully charge a good battery on low charge. (Avoid high charge rates with older batteries).
Your car uses an engine computer that takes 20 minutes to go to "sleep mode" after turning the engine off. During that time it can often be heard singing to you by the left front wheel, and it is draining the battery. Your dome lights are not operated by a simple, reliable door switch. They are run by a body computer that gets confused when battery voltage is low. You are paying the price for the manufacturers' unnecessary use of complicated, unreliable computers. This is why I drive a 1988 Grand Caravan - simple and extremely reliable.
Before you get too involved with diagnosing a problem you might not have, fully charge the battery on the slowest rate for 2 - 4 hours. After charging, turn the charger off, turn the headlights on for about 15 seconds to remove the "surface charge" which can lead to inaccurate test results. With everything turned off, measure battery voltage with a digital voltmeter. Anything over 12.6 volts indicates a fully charged battery. At that point, all the computers should work properly.
The next time the car will sit for more than a few weeks, remove fuse # 5 in the Junction Block on the left side of the dash board. It's in a yellow pull-handle. This is what's used when new cars sit in parking lots for months until they are shipped to a dealer.
Push the fuse back in before you drive the car next time. You will need to reset the radio stations and clock, and drive the car to perform relearn procedures. If the engine will not stay running at idle, drive at highway speed, then coast for at least seven seconds without touching the brake or gas pedal to relearn minimum throttle. The transmission might shift weird too for the first few miles until the computer relearns the characteristics of your transmission.
All computers will reset to factory-programmed starting values, and will update while you drive.
Thursday, March 26th, 2009 AT 4:50 PM