Hey, I just wanted to get back to you guys on how I made out. I put in the new battery and I was very surprised. I expected other things to be wrong, but when I engaged the PTO everything was fine ! I did scrape away all accumulated mulch on the mower deck, inspected the belts, etc. But it was just because of the battery. Thank God, it's one less thing I have to work on.
Thank you guys for all of your help !