I have been using Optima AGMS in my boat. 3 12volt in parallel in closed compartment for 3 years. Charging about every 2-3 days during summer. Only open the bottom at year end to disconnect for storage. Never had any problems.
And hopefully never will. As noted earlier on in this thread, as long as everything is working as it should problems are very rare. However, individual experience is no guarantee there is no risk. 🙂
Steve and Andra
2012 F350 6.2 gasser SRW LB
Fab Fours front and rear in case we run into a rhino
2019 Northstar Laredo SC