Hello Darryl, With Li battery chemistry, a process called Lithium Plating occurs when charging a frozen cell. Intercalation into the lattice (how Li battery charges and discharges) is resisted and the current then causes a metallic deposition on the battery anode. Think of electroplating. Once this happens, it is instant, permanent damage to the cell.
There are natural internal stresses in charging and discharging Li batteries. That’s why they swell. A danger of the plating process can occur later in battery life. The plating, in the form of dendrites, can puncture the separator film due to the natural pressures and swelling, causing a short circuit. Any short circuit in a Li battery is bad. Think Samsung phone. Our solution is never let a Li battery cell drop below 0°C. We build battery packs in boxes and use heaters when required. 2 of the brands we carry have charge inhibit controls that prevent charge current when a cell is below freezing. Larry Crutcher Starlight Solar Power Systems On Feb 26, 2018, at 12:09 PM, Darryl Thayer <darylsol...@gmail.com> wrote: Hi Daniel and Larry, I have a LI-FePO system, Simpliphy 10 kWh it is on its third winter, the batteries are unconditioned but in a box. I am now concerned, as I worked as closely with Simpliphy as I could. They did not caution me about the operation in the cold. The batteries sit and have no load other than the charge controller. This is similar to Daniel's system except he has some loads that run down the battery. If the sun comes out the batteries will get a chance to charge. The charge controller is a Morningstar Tristar 150V MPPT 60 A (not using the roll-back feature) I think I should pay a visit to this customer's cabin.
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