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Lithium bank drained.. HELP!

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  • Lithium bank drained.. HELP!

    Hi all,

    Newb DIYer here in need of assistance!

    So here it goes: I am in the process of cleaning up the electrical system on my sailboat. The power consists of (8x) 138Ah Lithium batteries (specs below), which are charged by the alternator and/or an 815W PV array via Xantrex C40 charge controller.

    In reconfiguring the house breaker panel, I accidentally bypassed the charge controller, effectively connecting the panels directly to the battery bank.

    The next morning the bank voltage had dropped to 10.8V, having drained through the panels overnight I assume...

    The batteries held a ~14V charge prior to this incident. They still deliver power and the health status indicator on each battery still blinks green, although I don't know how much it tells.

    In the meantime, I re-connected the charge controller, correctly this time, as well as an automotive battery charger @10A overnight to hopefully get my batteries back up.

    Woke up this morning and batteries still only show 11.3V despite automotive charger saying it reached full charge. Furthermore, the bank voltage has dropped back to 11.1V since morning despite the panels being connected and flooded with sun.

    The system was installed a few years ago by the previous owner of the boat and was functioning fine beforehand.

    I'm worried I made a big mistake... Did I damage my panels? Or worse yet, fry the batteries? How can I get the batteries back up to full charge quickly but safely, if even possible?

    The batteries are Valence U-Charge Model #U27-12XP with the following specs: Group 27 / Nominal Voltage 12.8V / Nominal Capacity 138Ah / Peak Load 300A / Cut-off Voltage 10V / Max Charge Voltage 14.6V / Float Voltage 13.8V

    It also mentions that they are compatible with lead-acid chargers, and the 40A Xantrex charge controller (NOT lithium-specific) is tuned to match the bulk/float voltages specified on the batteries.

    Any advice would be much appreciated!

  • #2
    Do some searches on the internet. Apparently there are some videos that might prove useful. Also try the manufacturer. It appears to be LFP (Lithium Iron Phospate) which is close to fully discharged at 11.1 volts. The internal BMS may have detected a fault and prevented your charger from charging it. Did you measure the voltage when it was on the charger? It probably consists of 4 groups of cells that nominally would be at 3.2 volts each when full or 12.8 volts. It does say it has a low voltage cutoff and if working that should have prevented full discharge.
    9 kW solar. Driving EVs since 2012