912 ULS Battery Drain Zenith CH-701

Have you let the battery sit overnight not installed in the airplane? Make sure the battery is good first. Just checking the voltage may not be enough.

I agree. The battery itself may be bad. If not then pull some circuit breakers or fuses and isolate the problem.

If your charger has some sort of charge indicator on it, a good battery will see 14 + Volts while on charge.

Anything much below 14 V Charge indicates a dud/warn out battery.

Never persist with a weak battery - the cost (damaged start system) far outweighs the cost of a replacement battery.

It’s the same process regardless of vehicle, so here you go: https://shoptoolreviews.com/automotive/diagnostic-testing/parasitic-battery-drain/34587/