Thats handy, I might just bag one of those and a plug in fan. Makes it nice & simple.
Ta. Dave.
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you mentioned heat mats under the batteries. Where are your batteries located?
I know they do derate when the cell temperature gets below 20 degrees C, depending on BMS firmware version - which is part of why I have gone back to BMS 3015.
Personally I’ve not experienced really low temperatures with my battery cells. The batteries are inside the garage, on an outer facing wall, but just being in the garage means the ambient temperature rarely drops below 10 degrees C and with regularly using the batteries the cells are usually 15+
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My (two) batteries are fastened to the inside brick walls of my garage about 40mm from the floor. I unscrewed the plastic feet from the bottom of the batteries to leave a perfectly flat metal bottom. Then I trimmed a piece of Kingspan so that it slides between the floor and the battery with a 7W Vivarium heater sandwiched between the Kingspan and bottom of battery. Works a treat. Controlled via a 2 channel Dingtian Ethernet relay - 1 channel heating, other cooling. I also have a single plastic covered Kingspan cover for the 2 batteries, which slides on in winter and off in summer. To be honest, the heater is not really needed now that inverters don’t throttle below 20 degrees, along with working them hard and controlling charge rates so that charge lasts the full 6 hours at night.
The thing is that the heating and cooling is there, even if it doesn’t actually kick in, it gives peace of mind.
Here’s temperature from last couple of days. Not dropped below 20. Even at sub-zero temperatures, I’ve only seen it drop to my chosen minimum of 15 degrees a couple of times this year, and that’s only for a few minutes. Placing batteries at the bottom is the ideal position because the bottom bank of cells is always naturally the coolest, so heat is gently applied where it is needed. Looking at these temperatures, it’s probably time for me to remove the covers after this cold weekend ahead.
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Yes, I kingspan my battery in winter too, only 50mm, but it’s enough.
Battery is 450mm off the floor, so well away from the chill concrete, and gives me plenty of room under it.
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Interesting thanks guys
here’s my similar graph for the past few days, cells sitting between 14 and 20 degrees
I’d always taken the view that my batteries were sheltered enough to not need a kingspan box making for them (different story if they were outside), but seeing yours, I think I’ll reconsider.
There is an almost constant 2 degrees C temperature variation between the cells, progressing from cell 4 up to cell 1 in the 9.5 battery, matching the battery stack, coldest at the bottom. The 5.2 which doesn’t get worked as hard its cell 3 that is always the coldest but there’s only 2 cell packs in the 5.2 so the temperature probes must be 2 per pack. My 9.5 is lowest to the ground but I think I can get some kingspan underneath it so I’ll probably try that first and see what difference it makes
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And now about low battery temps !!! Nnnoooooo ! 
Dave.
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So what’s the optimum temperature range for the batteries to be at ?
Dave.
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20 to 30 degrees in an ideal world.
5 to 45 degrees are what I would treat as the limits.
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Many thanks.
Dave.