Is it normal for battery temperatures to rise and then not fall in a battery box?

[WorldwideDave]

12V system. 200Ah custom battery. In plastic box with 5 sides (top open), and on a wood shelf with 4 sides open (one side is open for fresh air, and the top is open for about 8" above the battery cells and BMS).
My system has 2 battery sensors. One connected to Victron GX, and the other a Ruuvi temp sensor, just to compare.
I turn off all MPPTs.
Using AC/DC charger, I ensure both Victron Shunt reads 100% SOC, and the internal battery BMS (JBD) reads 100% SOC. The charger reads float, all is good.
At the beginning of the day, the ambient temperature is 11.5 degrees C.
Both temp sensors report around this temperature (12-13 degrees C) before any loads run.
I then turn on my non-victron inverter, and run a load at 160 Amps discharge. The pool pump runs for an hour at 3450 RPM, no problem. Around the 90 minute mark, Cerbo GX reports a low state of charge, followed by low voltage, and the BMS reports 0% SOC as well, and the voltage I think hits 11 volts and inverter beeps, so I shut off the load, and wait for inverter to cool, then shut off the inverter, and done with discharge test.
During test the temps go up to 38 degrees C max, or about 100 degrees F. No big deal.
I then wait another 90 minutes, but temp has barely gone down. It is still around 21C outside, but the temp sensors are still up at 30C. That is 9C or 48.2F difference from outside temp.
No the inverter isn't in the same space.
It seems to me it should be cooling faster than it is.
So after this discharge test is done, I leave the inverter off, I turn on AC/DC charger (25A victron), and turn on 3 MPPTs (2 victron, 1 non-victron) and pump as many amps as possible into the BMS to see what happens. First time ever charging at over 70 A - was exciting.
Peak amperage to the battery was 116 A which may not be super exciting to most of you, but my system used to overheat with anything over 45 A charging. Swapped BMS, FYI.
Anyway, as you can see below, the temps did rise, but only up to 36 degrees C. The sun was setting so that ended this test. The higher the amps charging (or discharging) the higher the temps would get at the battery.

This shows me that temps rise whether charge or discharge. Assumed that, but wanted to prove it.

However, even after turning the PV and charger back off, it has been 2 hours, and it still hasn't gone down below 32 degrees C.

Is this normal? Is this unexpected?

It is currently 14 degrees C outside right now. Temp sensors are twice that.

Just seeing if this is what I should expect - they don't cool down to ambient super fast.

I of course could add a D/C fan to blow air through the battery compartment/box, but if I don't need to worry about it - because my temp sensor is not reporting over 50 C - then I guess I will just let it go.

My plan is to discharge now to dead, then at peak sun tomorrow, charge again from cold and report back.

 

[chrisski]

That looks normal temp swing to me.

I wanted to post a graph of my data, but for some reason, the system does not log battery temp anymore.

 

[WorldwideDave]

That looks normal temp swing to me.

I wanted to post a graph of my data, but for some reason, the system does not log battery temp anymore.

Thanks you. Doing discharge again now. 41 C is max I hit.

 

[WorldwideDave]

Well, rainy day here. Low SOC and Low voltage. Hoping BMS disconnect kicks on. Pool pump ran anyway on schedule. Just before inverter kicked off:


and after:



I have all PV shut off, so small load from Outback FM80 SCC is only load + victron gear.

I think that the battery voltage slowly climbs back up when it his 10V.
As I type almost to 11 V.
I think the inverter will try to come back on, but not sure if it does that automatically - I don't think so. I have a remote button. Giandel 12V 2000W.

With nothing charging it, inverter should remain off.

With parasitic load, maybe by dinnertime the battery BMS will kick off. The thing is that it will kick back on automatically a few seconds later which I like. This should repeat for a while.

I was planning on firing up my PV and AC/DC charger to do another max charge situation, but terrible weather. May move around some panels today in the rain instead - what could go wrong
<watches Will's latest video on electroction for dummies>
Okay so not a lot can go wrong, except DEATH
Not working on jack today in the rain.

 

[HRTKD]

Batteries are quite dense. Once at a certain temperature they tend to hold that temperature, especially if there isn't a way to shed the heat.

My cells in a well insulated situation don't require much power to the warming system to keep them warm.

 

[J.H.]

Batteries are quite dense. Once at a certain temperature they tend to hold that temperature, especially if there isn't a way to shed the heat.

My cells in a well insulated situation don't require much power to the warming system to keep them warm.

Sorta the reverse of block ice holds temp as its density …my batts require very little heat especially if they are working, in my well insulated box .
It’s actually kinda mind boggling how easy it it is to keep them about 60 even in Zero F temps .
Third year doing it and I learn more each year…

Insulation is the key…

J.

 

[MattMan119]

Here is a few days from my home assistant from my battery … things look pretty normal to me also..

 

[WorldwideDave]

Thanks everyone. I think this issue is closed. I have successfully discharged at 150+ amps for a few hours at a time and had zero overheating issues.
I am going to rearrange some ground mount arrays to get better amperage from the MPPT to the bus bar - I am trying to get close to a 150A charge, but so far haven't more than 130 A out of my 2 ground mount arrays. Going to rearrange some panels this week (rain expected) and see if I can get output closer to 150A, then run loads to drain the battery down to low SOC and see what happens when I go to charge - will turn off inverter as well for zero drain of amps from battery due to idle consumption from the inverter.