Battery Dies Overnight
A battery that goes flat overnight has a parasitic drain, not a bad battery, unless the battery is already old. Test the drain before buying anything.
What it feels like
- It starts fine after a jump but is dead again the next morning
- The lights are dimmer than usual before you crank
- A clicking sound instead of a crank
- It started happening after you installed an accessory
Codes that usually produce this
Check these first, in this order
Free checks first. Nothing here costs money except the fuel you burn.
- 1
Measure battery voltage at rest with a meter on the posts under the hood after an hour of sitting.
What you'll see12.6V or higher. Below 12.4V means the battery is discharged or failing.
- 2
Measure voltage again while the engine idles with the alternator charging.
What you'll see13.8V to 14.6V. Below 13.5V means the alternator is not keeping up.
- 3
Disconnect the negative cable and put a meter in series to measure current draw with everything off.
What you'll seeUnder 50 milliamps after the modules sleep for 30 minutes. More means something is draining.
Stop and get it looked at if
- The battery is hot to the touch or smells like rotten eggs.
- The alternator belt is squealing constantly.
- You see acid leaking from the battery case.