Help this is my third Optima battery that has gone bad. They last about 6 months under light use. My only guess is my Bank Charger is knocking them out. The Optima site says to use AGM setting on the charger which is a Minn Kota bank charger. Should I change the setting or get a new Bank charger? I use a Noco Genius on my other boat.

We used them (starting batteries) a couple years on our fleet, nothing but problems. Cancelled them and went back to Interstate....

You did not say which Optima you are using but my experience with the Blue Tops has always been great for troll motor use. They do not hold up well for engine and electronics. MinnKota on AGM setting is fine.

If your charger has an AGM setting you need to be using it. AGM's require higher voltage to charge. Using lead acid setting won't fully charge it and will kill it in short order.

I found just the opposite to be true for me. They couldn’t run my Ultrex for more than 7-8 hours, but I have an 8 year old Optima Group 31 from my boat as my cranking battery in my Tundra and it’s been good for that when it seemed like it was dumpster time as a trolling battery.

Using a Blue Top for Trolling Motor

I am using AGM setting on my charger. It runs fine then one afternoon I go out and it is dead, after being plugged in all night and day.

Not uncommon for AGM's to cr@p out like that whereas lead acids have a long painful death.

You might want to check if your minnkota has 10 amp per bank

I’ve been using optima blue tops since 1996. Made in USA and Mexico, I never had a battery “die” before seven years of usage. You must charge as quickly as you can after getting off the water, you must have a charger that has 14 volt minimum and 10 amps per bank.
I have never used an onboard charger, I never felt they could take the abuse, I had Guest portable chargers for ever, but using single NOCO 10 genius for each battery now.