01
Putting the house bank on the cranking circuit
Lithium on the start battery’s bus means the alternator sees an infinite load after every stop. Keep the start battery lead-acid and separate, and join them only through a DC-DC charger.
Day boat · four to six aboard · 12 V
Bowrider Lithium Battery System
The bowrider’s house load is a stereo, an esky fridge and a lot of USB ports, all running while the engine is off at the sandbar. The problem is not capacity. It is a big sterndrive alternator meeting a lithium bank that will accept everything it makes.
Typical load profile
Stereo and amplifier20 Ah
Portable fridge15 Ah
Device charging8 Ah
Lighting (nav, courtesy, underwater)5 Ah
Bilge and blower2 Ah
Stereo draw is the surprise on this hull. A four-channel amp at sandbar volume is a fridge and a half.
What we would fit · 100 Ah
Budget build
$1,600
100 Ah drop-in LiFePO4, 12 V
25 A DC-DC charger from the engine
Lithium-profile 15 A mains charger
Fused battery switch
Separate cranking battery retained
Premium build
$3,200
200 Ah LiFePO4 with Bluetooth
40 A DC-DC with engine-run detection
Shunt monitor at the helm
Dedicated house distribution and fusing
Certified install and paperwork for the insurer
Indicative installed prices, September 2026. The DC-DC charger is not optional on a sterndrive: the alternator is large, internally regulated, and expensive.
On this hull specifically
Battery installation mistakes for this boat type
02
Sizing on peak stereo, not on hours
Owners quote the amplifier’s rated watts. What matters is the hours at the volume you actually run. Measure a Saturday with a shunt before buying 300 Ah you will never use.
03
Skipping the battery switch
A lithium bank with a Bluetooth BMS still drains through the stereo memory and the bilge float over a month on the trailer. A switch, and a habit.
04
Ignoring the engine maker’s charging notes
Mercury, Volvo Penta and MerCruiser all publish what they will and will not warrant with lithium on the charging circuit. Read it before you wire it.
Other hulls