Did you get an onboard battery charger?
Highly recommended. I thought they were kind of a scam, but I bought one anyway.
Kind of a scam in that they're expensive as far as chargers go, for sure. And quite convenient.
When my best fishing buddy bought his Riptide used, it came with a 10 amp (5 X 2) onboard (I, being the ex-Battery Guy, installed everything). At 5 amps a side, the only real complaint is it's a little slow for use on consecutive days, especially when we run the 4 battery setup on the 24v motor (too heavy, but lasts all day and then some). The 10 X 2 models is definitely better, but they cost about twice as much. But the alternative seems to be to use an automotive charger or two, which requires finagling with the wiring each time you charge (not what you want to do at the end of the day). Or a series charger which can handle 24v or 36v, but that's also an expensive option, and couldn't (shouldn't?) be mounted onboard.
So, while the onboards are overpriced for what you're getting, they're still the best option. The 24 volt (or 36v on the 101# models) thing really limits the options if you don't want to mess around with changing wires every time.