Draining battery

Monte Carlo, 6 cylinder, 1999

What could be draining the battery on a regular basis? The battery is being drained and no one has found the source. This is not dependent on weather.

We have been advised to replace the battery 3 times this past year. The mechanics say the alternator is functioning properly. All electrical systems appear to be functioning normally. However if the car sits for three days, the battery is discharged. The lights such as the trunk and glove box have been checked. The turn signals and exterior lights have been checked for dead shorts.

I once had 1966 Jeep that was draining backwards through the alternator. Is this possible with this engine?

Someone is going to have to start pulling fuses, one at a time, and then seeing if the draining stops. Maybe you can locate the short. It can also be done with appropriate meters which can test a circuit for current flow.

First thing is to isolate whether its the battery or a drain on the battery. Disconnect the battery cables for three days and see if the battery drains down. If so, the battery isn’t holding a charge and needs to be replaced. If it is ok after being disconnected, then put a test light between the positive cable and terminal. It will glow if there is a load on it (some dim light is normal). Pull the fuses one at a time until you find the circuit that turns the light down. Once you find the circuit, you’ll need a schematic to see what is in it and start disconnecting the devices or checking the wiring till you find the problem.

Some places to suspect would be cig lighters, load leveling device, interior light devices that go on and off and you don’t know it, and so on.

To drain a battery in three days there has to be a load of at least a half amp. This could be seen with a small lamp in series with one of the battery cables. Normal battery currents will be less than .03 amps. this current can initially be higher for about 15 minutes in those vehicles with battery saver circuits that power a relay.