A boat’s house bank lives the deep-cycle life in its purest form: days at anchor drawing down on lights, refrigeration and instruments, then a long engine or shore-power recharge. It also lives it in the worst mechanical neighbourhood — vibration, heel, heat in an engine-adjacent locker, and months of winter storage. XD Battery’s deep-cycling series is documented across RV and marine service (the company’s 12V leisure lines serve RVs, caravans and motorhomes as a named category), and the gel branch of the family is the marine specialist: sealed against heel and spill, indifferent to orientation, and free of the watering routine a boat will not perform.
The two-battery discipline is the first rule afloat: the engine keeps a dedicated starter battery; the house loads live on the deep-cycle bank; a split-charge arrangement (or DC-DC charger) lets the alternator feed both without ever letting the house loads touch the starter’s reserve. Every experienced boat electrician rigs it this way, and every "battery problem" that strands a boat traces to rigging it the other way. The second rule is sizing honesty: refrigeration dominates house loads, and the bank arithmetic from the solar pages applies unchanged — daily amp-hours, 50% design depth, matched blocks, one age.
Choosing the house bank
- Attended, ventilated locker, budget-led: deep-cycle blocks from the 12V line
- Hot, tight or heeled installation, minimal attendance: the solar gel models
- Larger yachts and RVs: 200Ah-class blocks to cut parallel strings
- Always: one model, one age, and a charging source that can actually refill the bank between uses
Can one battery do starting and house duty?
It can, briefly, and then it does neither well. The two-battery discipline exists because the duties are opposites; combination batteries are a knowingly-made compromise for the smallest boats.
How should the bank winter?
Fully charged, disconnected, and topped up periodically — self-discharge never sleeps, and a discharged battery in freezing storage is a spring replacement.