S: Car doesn’t crank over. Battery regularly loses juice.
C: Likely cause – drained battery / short circuit in the system.
Test voltage on the battery – anything below 12v is bad news – try to charge it up. (some notes coming on how to verify battery’s charging ability based on amps)
To test for short circuit in the system, do the following:
1. Visually inspect positive cables leading away from the battery.
2. Unplug the negative terminal of the battery.
3. Wire up a 2-5 watt 12v light bulb. Place one wire on the negative terminal of the battery and the other on the disconnected negative terminal. With car off, if you get the light bulb to light up even a little, you got a short circuit somewhere. Intensity and the bulb you choose can indicate roughly how much drain there is – brighter = more flow / less resistance.
3. To further test where the short is, uplug one fuse at a time until the bulb shuts off. When it goes off, inspect the system or wiring associated with that fuse.