How to Store Boat Lithium Batteries Over Winter

How to Store Boat Lithium Batteries Over Winter: steps

Bring it to a partial state of charge
Use the storage figure from your pack's datasheet, typically somewhere around half. A bank left full ages faster, and one left flat risks dropping to where the BMS will not allow a charge.
Disconnect the parasitic loads
Bilge pump memory, alarms, stereo standby and gas detectors all draw quietly for months. Either isolate them or plan for what they will consume over the lay-up.
Do not leave it on a float charger
Holding lithium at full for a season is the single worst thing you can do to it. If the boat stays on shore power, turn the charger off or set it to the storage voltage.
Think about the temperature it will sit at
A closed boat in an Australian summer gets very hot, and heat at high state of charge compounds ageing. Cooler and part-charged is the target.
Check it part way through
One voltage check mid-lay-up catches a parasitic load you missed while there is still capacity to recover from it.
Bring it back up before you need it
Charge fully and let the monitor re-synchronise before the first trip, so you start the season with an accurate gauge.