Earlier today I tried the battery and jumped it. Fired up. I don't know how the battery became dead because I don't have to jump the mower to start it. Weird. At least all I have to do is replace the pulley now.
Get the output of your alternator checked.
Electric clutches draw a lot of power and what is happening is the battery is supplying electricity faster than the chemistry can cope with so your battery appears flat.
Left alone for a while the chemistry equilibrates and you can draw some more power out of it. Same thing as flattening your car battery by leaving the headlamps on.
Often if you leave it overnight there will be just enough recovery to crank the engine over & maby even start ( unless you are cursed like me ).
However if you flatten the battery slowly by leaving an internal lamp on, there will be no recovery and in the worst cases the battery will not be able to be recharged without a lot complicated procedures.
You have had the exact same thing happen with that torch which went flat and you forgot to get new batteries for.
You take it out of the draw and if by magic you get nice bright light,,, for 5 minutes.