Battery mystery

[Ken Pole]

My boat was hauled Saturday for her winter on the hard (198 days until Launch 2022!). The Atomic 4 started up fine the day before so that I could move her from my slip to the haulout area (we bring in commercial cranes).

When I returned yesterday to drain and flush the engine preparatory to running antifreeze through it, I found the Oasis Firefly AGM flat. I have two but had taken one home for winter storage. It was connected directly to the starter -- no switch and all electronics off the boat for an electrical panel rewiring.

I'd be grateful for any suggestions as to how this could occur. Thanks in advance.

[Madehn]

My guess would be a key switch that stuck in the run position even with the key out Happens once in awhile.

[smac999]

A bad alt can drain current. Charge it up. Reconnect. And measure for drain

[Ken Pole]

Thanks for both responses. For what it's worth, I don't have a key, just a pull/push on-off switch and a starter button (a common A-4 setup). Will explore the "bad alternator" situation but can't wrap my head around the fact that the only connection between the battery and my starter was direct cables.

[capt jgw]

Is the alt output connected to the starter battery cable as most are? That's how a bad alt could drain the start battery. If connected direct to the house battery as some are, it would drain that one. Barring that I'd look at the on-off switch. Being on an A4 it must be pretty old, there could be corrosion bridging the contacts. Not enough to let the engine start in the "off" position, but enough to drain the batt.

[Ken Pole]

Thanks. I think the switch is original so, yes, old. I'll replace it and see what happens.