Speaking of batteries...
usually needs (6) 6v batteries every 1-2 years.
That’s sounds like a pretty short life for deep cycles? Should be getting at the very least 3 years with heavy use. With light use closer to 4 or 6 years? Something doesn’t sound right. The right charger is important. That smart charger might help. Always store them fully charged. If you were over charging them that could lead to an early death too. So could not maintaining the water level (distilled water).
I guess time will tell but I’m not sure you’re doing yourself any favors by knocking off 300 lbs. of battery with the same deep cycle lead acid batteries… I think it’s as true with batteries as it is with most things…You get what you pay for.