Thanks for the info!

After going over the voltages again after dinner, it looks like the charger is
only putting out 18-21VDC, which is too low to give a decent charge. Seems like
I remember troubleshooting something else on this mower a few years ago and it
was putting out 27VDC.

So, I went back and look at the little rectifier board, which is just 4 diodes.
The input there is 35VAC and the output is 107VAC and 46VDC. Does this look
weird? I'm wondering where the AC is coming from and why it's up so high.

The diodes all checked out OK with an ohm meter, but I’m wondering if one of
them is breaking down when AC is applied (?)



"AWM"

If it is a 24 volt battery (a thing Ididn't know existed -- any time I have
come across 24 systes they have always been 2x12 volt batteries) it needs
about 28 volts output from the charger, and the fully charged battery should
show about 26 volts acroos the termminnals of charge.

It looks to me like one of the dodes is blown in the rectifier pack, i
would just replace with a single solid state rectifier.