Check your batteries for boiling.
I chased the same problem, same symptoms, etc, for a while.
Turned out the batteries were bad.
They'd accept a full charge, but be dead the next morning.
And the charging system was constantly putting out 15v or more.
Finally I noticed that after they had been charging for ten minutes or so, they were boiling. You can barely tell. You really have to pay attention.
Replaced the batteries and everything was fine.
I chased the same problem, same symptoms, etc, for a while.
Turned out the batteries were bad.
They'd accept a full charge, but be dead the next morning.
And the charging system was constantly putting out 15v or more.
Finally I noticed that after they had been charging for ten minutes or so, they were boiling. You can barely tell. You really have to pay attention.
Replaced the batteries and everything was fine.