Hi 12VMan (and Victron staff please). I found your thread on Lithium battery protect settings while searching, but decided my comment should be a new question.
Thanks for your answer in that thread, mentioning that Victron lithium batteries issue a temperature alert at 5C. This gets my attention. My research to date was indicating that lithium batteries are OK for charging down to around 1C (and for discharging well below 0C, as an aside). I need to pursue this, as I'm planning to use Victron LiFePO4 batteries in Arctic conditions, in an expedition yacht that will be static for days to a week or two. Water temps will be down to around 2-3C, sometimes lower depending on icing. I'm looking into the need for heating for the battery box, which will be under the insulated floorboards and so outside of the primary heated spaces. If 5C is the real deal, I need to get serious with calculations on battery energy that might be consumed in making the batteries warm enough to be chargeable. Or other heating.
So, where is this 5C figure coming from? OK, I see +5C mentioned in the 12.8V LiFePO4 battery data sheet.
This prompts a few specific and important questions, about the Victron 12.8V 300Ah variants:
1. What is the lower internal battery temperature at which the battery signals to a connected BMS that charging is not permitted?
2. If the answer to Q1 is different than +5C, what is the consequence in terms of battery health (and charging efficiency?) of charging occurring between the two temperatures?
3. Does the answer to Q2 depend on the rate of charging?
4. If the internal battery temperature is just high enough for the battery to allow itself to be charged, and in this case at a low rate of 20A per battery (80A from a normal alternator, shared between 4 batteries), will this charging slowly warm the batteries up such that a higher rate of charging can be initiated in due course?
5. At what battery temperature (measured by a sensor on the positive terminal, or is there a way to get the internal temperature?) can high rate charging at ~150A per battery be initiated, such that no appreciable damage to battery health occurs? Would it be prudent to step the charging rate up slowly as the batteries warm up?
Clearly, it will be helpful if I rig a temperature sensor for the battery box, to guide appropriate action before each charging session.
The boat will use an Integrel On-Engine Charger (basically a big and very efficient second alternator) which can charge at up to a very high rate. Or it can be turned off so that charging is via the engine's standard alternator only. I might need to raise the battery box temperature before starting to charge each week or so. Heat from the main engine during these charging events will then help.
Thank you for your help with these questions. :-)