Found this which may help
Current drain on the battery can be checked with an ammeter. Make sure the ignition is off, then disconnect one of the battery cables. Connect one ammeter lead to the battery and the other to the cable. The normal current drain on most vehicles should be about 25 milliamps or less. If the key-off drain exceeds 100 milliamps, there's an electrical problem that requires further diagnosis.
Finding the hidden current drain can be time consuming. The easiest way to isolate the problem is to pull one fuse at a time from the fuse panel until the ammeter reading drops. This will tell you which circuit is draining the battery. Then you have to check the wiring and each of the components in that circuit to pinpoint the problem.
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