They look very interesting. Especially how they can series up to 72V. The prices make me a little concerned on quality. I would ask where or how they work at -13F for sure. I don't use ANY lithium that doesn't have a built in heater. Charge at Cold ( -20C) even slowly will destroy them after the next cycle.
Cold temperature charging fatigues all battery cells, this is not an issue inherent to "Lithium" cells. However, each battery chemistry is more or less effected than others; NMC cells for example are quickly and severely damaged, these are the batteries that run most EV drive-trains, cheap and very high energy density. LFP and AGM are both much more stable and fatigue much less by deep cold charging. The big questions to ask in setting up a system though: How cold? How many Amps is the charging going to be in that cold? How cold is it during charging? (when talking renewables/solar this is important consideration)
How cold?
It is easy to assume the outside temperature is the same as the battery temperature and base things on that, however that is truly worst case scenario. In Tesla vehicles, for example, the 12V battery is located up front, under the frunk liner near the front-wheel electric motor and top of the main traction battery pack (Model S and X); this location actually never gets as cold as the outside temperatures (unless vehicle is totally discharged and left in extreme cold) because the main traction pack is being heated all the time to protect the cells (NMC style, WAY more sensitive to cold), some of this heat is radiated into the surrounding space.
Another example is the Sprinter-chassis campers, the Aux/House battery is located in the engine bay, during driving (when they charge) the engine is running and warming that bay up quite a bit.
In a boat, the battery room may be located near a generator room or engine room, these generate heat, the battery room itself may also be insulated from the outside temperatures and low enough in the boats hull to be warmed by the sea-water it is floating in.
My point is: unless you are planning to install the battery in an open-environment analyze the temperature extremes based on its installation location conditions and not the climate conditions (to a point).
Ohmmu does "deep cold" testing at -30C (-22 F) to -20C (-4 F). These tests are done in-house, the batteries (or cells alone) are put into a Thermotron unit which brings the unit to temperature and holds it there for weeks while the battery is cycled, it is charged and discharged in sequence back and forth. After several weeks in the cold cycling the battery is brought back to 25C (room-temp) and then cycled to assess capacity degradation caused by the deep-cold cycling. While losses DO occur (the total capacity will decrease) it is in line with or better than (less loss) an AGM battery in the same test conditions. Like I said, all batteries lose capacity in these situations, the questions are "how much?" and then assess how much is acceptable to the application and conditions.
How many Amps?
The thing that fatigues batteries the most in the deep cold is charging, discharging is really not an issue, it is effected (cranking Amps drops) but the act of discharging during cold temperatures doesn't fatigue the battery in and of itself, that is from charging. Charging, throughout a batteries life, is one of the most important things we can do to retain battery health. Charging is what fatigues (damages) a battery and reduces its capacity. How fast do you charge, What voltage do you charge up to and what conditions are you charging in; these are all critical. Charging at high-speeds fatigues a battery, just like charging at deep-cold, charging at high-speeds in the deep-cold of course is a double-whammy and really destroys a battery FAST (why a Tesla Supercharging station will first heat the battery if needed before pushing big amperage). In the deep-cold, of course, one would want to charge at low rates to further protect from battery fatigue. "low rates" of course is subjective and completely relative to the battery capacity, a very large battery capacity can handle a lot more charging current. My recommendation is that if charging is to occur below 32F then the current should be less than 20% (30A for a 150Ah) of the capacity and as the temperature of the battery drops that current limit also drops. at 20F I'd recommend keeping it below 10% (15A for 150Ah) of the capacity, below 0F I'd stay below 5% (7.5A of 150Ah) of capacity, below -10F 1% (1.5A of 150Ah) should be the limit.
How cold during charging?
So, with solar energy charging one must consider when that charging will happen. Is this current coming to the batteries at "over-night low" temperatures or when the sun is out and shining and warming everything up? Obviously, it is the latter and this is in our favor because it means the battery cells will be operating at a warmer temperature during this type of charging, which is always a good thing!
OK, I spilled a lot of info here, hope it is helpful to someone out there!
