AGM, not flooded
Lifeline is an absorbed-glass-mat line. You cannot add water. Charge voltages follow AGM, not flooded equalization habits. Battery University’s AGM notes — spill-proof, vibration resistant, heat-sensitive — are the right frame for a sealed house or starting pack in a closed box.
House and start
These show up as house banks on sailboats and cruisers, and as starting batteries on boats that want sealed cells and a firm hold-down. An 8D is a large, heavy case. Getting it through a cabin hatch is the labor, not the brand name.
Charger first
If the onboard charger is still set for flooded wet cells, an AGM Lifeline will be overcharged or undercharged depending on the program. We read the charger before we talk about group 31 versus 8D.
Lines we are asked about
Model names below are public line names used to identify batteries already on boats.
- AGM group 31 class — Sealed AGM in a group 31 envelope for house or dual-purpose, depending on the model.
- Larger AGM 8D class — Big AGM house batteries on cruisers and sailboats with room and an AGM charger.
We replace marine batteries at the boat. See services and what changes a quote.