Small Engines (Lawn Mowers, etc.): Bush Hog 2560; battery not holding charge, bush hog, kohler engine

Question
I have a Bush Hog model 2560 with a 25 hp kohler engine. I am having trouble with the battery holding a charge. I just changed the battery on this mower and after using it a few times (I have rental property so it gets used often) the battery is dead again.  I can charge it and it will start for the next few times I use it.  I tested the starter as well as the fuses and they are good.  Do you have any ideas?  Thank you so much.

Answer
The first thing you need to do is verify the alternator is working.  This is pretty easy to do, just check the voltage of the battery, fully charged, with the key off and again with the engine running.  There should be a jump of 1-2 volts running.  If you can check this and let me know what you get we can go from there.  Thanks, PK.