01
Letting the house load sit on the start batteries
Modern outboards need clean voltage to start and to keep their ECUs happy. Isolate the house bank completely and feed it through DC-DC chargers.
Long days offshore · twin outboards · 12 V or 24 V
Offshore centre console Lithium Battery System
Big electronics running all day, livewells and bait pumps that never stop, and a pair of outboards whose electronics brown out if the house load pulls the start voltage down during a restart. The bank here is about voltage stability under load as much as capacity.
Typical load profile
Twin plotters, radar, sounder48 Ah
Livewell and bait pumps30 Ah
Fridge or icebox chiller18 Ah
VHF, AIS, stereo8 Ah
Lighting and device charging6 Ah
A twelve-hour day with everything on. Lithium’s value here is holding 13 V under the pump load while the plotters boot, which AGM stops doing at half charge.
What we would fit · 200–300 Ah
Budget build
$3,800
200 Ah drop-in LiFePO4, 12 V
40 A DC-DC charger from one outboard
Isolated cranking batteries retained
Class-T fusing and heavy cable
Shunt monitor at the helm
Premium build
$7,900
300 Ah LiFePO4 with CAN telemetry
Two 40 A DC-DC chargers, one per outboard
Lithium-profile 40 A mains charger
Full NMEA 2000 battery data on the plotter
Certified install, insurer paperwork
Indicative installed prices, September 2026. With twin outboards, one DC-DC per engine keeps the charge going when you run on one motor.
On this hull specifically
Battery installation mistakes for this boat type
02
Undersized cable from the transom to the console
Long runs at 12 V drop voltage fast under pump load. Size the cable for the current lithium will let you draw, not for what the old AGM managed.
03
Assuming the outboard alternator can charge 300 Ah
A 60 A outboard alternator sustains perhaps 30 A. Into a flat 300 Ah bank that is a ten-hour charge. Solar and shore power do the rest.
04
Skipping the low-temperature cut-off
Pre-dawn launches on the south coast in winter are below the charging floor. The BMS needs to know that.
Other hulls