I bought two Duracell AGM group 24 batteries from Batteries+ for about $198 each. The Optima yellow top batteries lasted about 8 years. Life on a trickle charger is good.
12/19 Update: one of the Duracell AGM group 24 batteries lost capacity after two years ( but not enough for warranty coverage ). The symptom was low voltage warning on chart plotter after two hour day sail. The batteries were actually one year old when I bought them. For reliability I replaced them with two Gel cell group 24 that were manufactured in November 2019.