My car battery dies overnight
My car has 105000 miles.
My car has an automatic transmission.
First things first, Have the battery charged and then load tested. If you have never put a new battery in your car it's probably about time. When you're satisfied that you have a good battery in the car, weather it's your current one or a replacement, the charging system needs to be load tested. It may be charging enough to keep the indicator out, but not all the way up to it's design capacity. Modern cars use a lot of electrical power, so the charging system has to be performing well. Then comes a test for off key draw. A low amp probe is placed on the battery cable and the car is allowed to shut down. This test takes some time because it takes about 20 minutes after you turn off your car for all the modules to "go to sleep." There will always be some off key draw, about 200 milliamps is common, to keep the modules alive, but a good battery should be able to keep the voltage up in spite of that for a few weeks at least. If the off key draw is in excess of 200 ma, then the source of the draw has to be foundand corrected. Most people don't have the time or the tools to perform these tests, but if you contact Your Mechanic they can send a technician to your home or office to check out you charging system and tell you what it's going to need.
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