House is the product on a sailboat
Lights, instruments, an autopilot, and a fridge are a night of amp-hours, not a cranking pulse. The starting battery should be separate so a dark cabin still leaves a way to start. BU-105’s reserve-capacity and amp-hour definitions are how we compare lead house batteries. Depth of discharge (Wikipedia) is how hard you use them each night.
Access is through the cabin
8D and large AGM cases live under a step or in a locker. The labor is the hatch, not the logo. Lifeline-style AGM and gel are common because they are sealed in a living space. Flooded house in a cabin still needs a hydrogen vent path. We look at that before we leave a wet cell under a berth.
Charging from shore, engine, and sometimes solar
A charger on the dock has to match flooded, gel, AGM, or LiFePO4. BU-409b is the lithium float warning. An alternator through a combiner has to play with that chemistry too. Mixed house and start chemistries are ordinary; mixed programs on one charger are not.
Inverters make the bank look small
A microwave on a 12-volt bank is a short, brutal load. If you live on invert, size for it or stop using that load at anchor. We would rather say no to a tiny gel bank plus a large inverter than pretend the numbers work.
Pinellas and Tampa Bay slips
We come aboard. Photos of the house bank, the charger, and whether the starter is a separate battery are enough to start a quote. Sail-specific spar work is not this visit; the batteries are.
Liveaboard versus weekend
A weekend on Tampa Bay with a small fridge is a different Ah number from a week on the hook. We size from the nights you actually do. If you are moving from gel to lithium, the charger and the combiner move too. The spar and the sails are not this visit; the bank under the step is.
Sources
- Battery University BU-105 — Battery Definitions (RC at 25 A)
- Wikipedia — Depth of discharge
- Battery University BU-409b — Charging Lithium Iron Phosphate
If this is the job on your boat, see how we replace batteries at the boat. We come to you — Florida towns and counties.