Riding mower would not start so recharged the battery, ran for several hrs then died , bought a new battery runs for couple hrs and quits again, again recharged battery again runs for a couple of hrs then quits.......?
The charging system is failing. It could be many things.
Check the fuse. Make sure there are no loose wires. Beyond that it could be a defective voltage regulator, diode or possibly the stator it's self. It may be one for the shop to diagnose.