Battery issue?

I have a G3 with a Yamaha 4-stroke 70hp motor. The motor was just recently completely serviced. I have separate batteries for the motor and Trolling motor. I have a 2 bank on-board charger. I always leave my battery charger plugged in. I showed full charge on both batteries yesterday, so I left to go the camp for a fishing trip this morning. To my surprise, the motor wouldn't start! It would barely turn over, sort of like a failing car battery. I decided to use the trolling motor, and it didn't work at all! Nothing! I was able to raise and lower the motor, and the bilge pump was working. I just got home, but won't be able to look into things until tomorrow. Any thoughts? Both fuses in the console looked ok. Not sure if there is another fuse on the battery cable, or not. I'm thinking that if a fuse was blown, it wouldn't have even turned over at all. Thanks, in advance, for your help!

Update......I came home, put both batteries on charge, and when they reached 100%, I unplugged the charger. I tested the trolling motor, and it fizzled out after a minute or so. The starter battery barely cranked the outboard motor. Should I assume that the batteries are both bad, and won't hold a charge? The month/year dots weren't punched out, so I don't remember the year of the batteries. I don't have a load tester. Could it be anything eles?
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The thing with onboard chargers is that most boaters finish boating and plug in charger till next time.nobody ever services the battery.if i had a dollar for every battery that had no water in it,i wouldn't have to do this crap