Battery drain

[FireFox31]

I need help finding the source of battery drain in Geronimo, the 2000 V70 NA automatic with 350k miles. I can charge the battery for 12 hours and the car starts great. When I leave it connected overnight, the battery can turn on the interior lights but only crank the engine once.

The battery is from August 2020, starts strong, reads 12.6V when off, and tested good at AutoZone. On my Schumacher charger, the charge indicator stayed at 99% for 12 hours which is odd (it should start at 50% and gradually rise).

I ran a parasitic load test by connecting my multimeter between the negative cable and negative battery post. It fluctuated between 14-17 mA with a spike to 20-24 mA every 2.5 seconds (the radio light blinking). I pulled every fuse and only saw the load decrease slightly when I pulled #6 (central locking, 20A) or #7 (radio, 20A), though still fluctuating. The draw dropped to 7 mA (no fluctuation) when I pulled 60A fuse #6 and oddly increased to 24-27 mA when I pulled 50A fuse #7.

I ran the same parasitic load test on my V70 and got very similar results. A low reading of 14-24 mA draw and seeing the same on my car suggests that there's no significant parasitic draw on the battery.

The positive cable in the small fusebox looks corroded, while it's in perfect condition on my car. The negative cable ground is broken at the transmission but has a thick grounding wire to the body near the battery. I suspect these cables could be the problem.

The alternator looks fairly new, though surely aftermarket.

What else can I check to determine why the battery is draining overnight? Thanks.

[abscate]

It could be internally shorted and drain itself overnight

Charge fully , with disconnect cables , let sit for 24 hours , and reconnect just before starting. Measure voltages each time too

Your current draws aren’t high enough to kill a goid battery. Anything under 50 mA ( 0.050 A) is ok

[FireFox31]

I think the battery is good. I charged the battery, let it sit disconnected for two months, then it started the car easily. I had Geronimo for all of December and disconnected the battery each night after working on it. I started it probably 16 times and drove only one mile after each start (so the alternator barely charged the battery). It started strong each time.

What's the correct way to do a phantom drain test? Are there any systems which turn on after a long amount of time has passed?

The front passenger's door doesn't lock when the lock button is pressed. After pressing the lock button, opening that door doesn't trigger the alarm. Any chance that's it?

Could the corroded battery cables be draining it somehow?