Working out battery capacity, Ah requirement and lithium on board

The sum is simple, the answer often comes as a surprise: a fridge drawing sixty watts uses 720 watt hours over twelve hours, which is sixty amp hours. With lead-acid the battery has to be twice that size, because discharging below fifty per cent ruins its service life. Lithium tolerates a depth of discharge of eighty to ninety per cent, so roughly half the capacity is enough.

In insurance terms, lithium-ion batteries are a subject in their own right. They have to be declared on the proposal, because they behave differently from lead in a fire. We do underwrite them. The battery, the charging equipment, damage from animal bites and short circuits are all covered under our electric and hybrid tariff, and so are the disposal costs of damaged batteries.

What matters is proper installation. A home-built battery pack without a battery management system is no argument in your favour when you make a claim, it is an argument against cover. Put the invoice and proof of installation in the boat's papers, and half the claims handling is already done.