Re: What to do with LiFePO4 batteries when the boat is layed up?

Joerg Esdorn

I started this thread with the question of what to make of the winterizing instructions in the manual for my MLI 5500 batteries, to wit:

„If the battery will not be used for a period exceeding 3 months, we advise the following:
• If external AC power is available switch off all loads and switch on the charger. Apply a float voltage as specified in the following table.
Model Float voltage setting
12V 13.5V 24V 27.0V
• If no external AC power is available:
- Charge the battery to > 80% of its capacity before storage.
- Set the safety relay knob to “LOCK OFF”, see page 11.
- Make sure MasterBus powering is not set to "Always on" (see Configuration tab in
In this setup the batteries can be kept at least 6 months without maintenance. However, it is highly recommended to charge the battery to > 80% of its capacity every 100 days.“

For this winter, I have actually disconnected the batteries as per “no external AC power available.”  But given the quote from Elon Musk above, I will believe Mastervolt that option 1 “if AC power is available” is also ok and wont damage the batteries.  Even more importantly, I will no longer hesitate to put the boat on the charger in a marina to charge to 100% and to make use of the full capacity (100% to 20%) of my batteries.   We’ll see how it goes!  Many thanks for everyone’s input.  

Joerg Esdorn
A55 #53 Kincsem
Currently in La Rochelle     

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