One of two things, most likely. The charging circuit is not working or current is leaking while the mower is idle. Troubleshooting these properly requires some testing gear including a basic electrical multimeter and some understanding of how to use it. If you had an external battery charger you could rule out the current leak by seeing if the battery held a charge both connected and disconnected to the mower cables.
I also wonder if the sink plug has anything to do with having the convenience of a garbage disposal. Here's where you get to blame the whole thing on your spouse like I do (hope Glenda isn't listening). Most folks don't understand that a garbage disposal is not meant to shovel massive amounts of food down it's gullet. It's mostly so you don't have to scrape your plates totally clean before washing them in a sink. The pipes do trap soap and grease which builds up and will then trap food when too much goes down at once. The worst episode we had many years ago was when my wife bought fresh corn on the cob at a farm market...husks, silks and all. I don't need to tell anyone what she did after shucking the corn but it required some dismantling of the plumbing to get things back to normal.
I'm having one of those days when it seems like everything is breaking.
I got back from my bike ride to discover that the lawn mower won't start. In the first place, it's hard to believe the lawn needed mowing in December, but never mind that. We tried to mow at Thanksgiving, but the mower wouldn't crank. It sounded like a dead battery so I went out and bought a new battery. No joy. I called the repairman who picked the mower up and returned it yesterday. Diagnosis: dead battery (the new one!). He charged it, the mower ran. He brought it back. Today the battery was dead again. We borrowed the neighbor's mower and mowed. Now the question is: Is the battery dead because of an electrical problem in the mower? Or did we just buy a defective battery?
My wife called me into the kitchen this afternoon because the sink wouldn't drain. I couldn't get it unplugged. In the process of trying I managed to make the garbage disposal (which is apparently the culprit) starting leaking from one of its seals. Maybe the plumber can get by Monday. In the meantime we're down one sink. At least it's a twin sink and the other side is still functioning. And the dishwasher is connected to the side that still works.
Even the tire pump for the bike didn't work right this morning.
It's just been one of those days.