Before I buy a new battery, I always try this: Put 2-3 aspirin in each cell, check water level of battery and fill to appropriate level with distilled water. Recharge the battery and see how it does. I have gotten as much as 3 more seasons from a battery that wouldn't do squat by doing this. Almost always get at least one more season. It even works on starting batteries. (sometimes) Many years ago a really old fisherman told me this. He was probably at that time about the age that I am now.
It doesn't always work, but is worth a try.

I think one of the things people overlook is how we charge them. There are definitely good chargers and not so good ones. I get the Minnkota chargers and it has electronic controls and feedback to ensure it doesn't overcharge them, which often kills them (even the good batteries). Just my opinion.

Best? Optima Blue Top AGM�s. Best Value? Walmart Everstart 29DC. https://www.walmart.com/ip/EverStart-Maxx-29DC-Marine-RV-Deep-Cycle-Battery/131118029

Atwoods has a deep cycle on sale this week .....
... DuraStart $69.99 ....

We run battteries on 5 boats and I�ve tries about every brand and have had best luck with the Walmart Everstarts!