Some advice please. I took my mini 2 for a flight yesterday, it has been two months since my last use. The controller had had three lights of charge showing and so I recharged. At about 8 minutes into the flight the drone executed RTH and I saw the controller had shut down. Any attempt to turn on, or recharge failed (even when left for several hours), no lights. On opening up the controller I measured the battery voltages at 3.11V. So I am wondering whether this low voltage could cause the shutdown and whether it is worth replacing the batteries? I have no warrantee but I have plenty of 18650’s of similar spec I could try.
A few controllers are compatible with the DJI Mini 2 @crispspark
Which controller are you using?
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Worth a try then 
On the back it says rc231?
Thanks, I thought it was but when I had a close look at the back. OK I may try charging the batteries independently to bring up the voltage and see if it is a bms shutdown first before trying different 18650’s.
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Epilogue :- Well I charged the existing batteries to 90% using a tiny socket and my imax b6. they held a charge overnight but when connected controller dead. I have another coming soon so hope that will solve my being grounded unless I get the spark out. 
Do you think the BMS has shut them down?
Possible but then how can I reset it? I tried a long charge. One video I watched suggested something on the main board self destructed if the batteries got too low and required a new board!! That did seem absurd. I’ll keep looking for a solution I like a challenge.
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Same here, I will keep looking as well 
I found this which shows a component that stopped the charging. (This STMicroelectronics SMAJ6.0A-TR, Uni-Directional TVS Diode, 400W, 2-Pin DO-214AC) However it did not help the poster as he could not turn controller on which is my problem of course. Another found a short on an IC but no further details.
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This video reckoned that diode was the problem.🛑😭 CONTROL DJI MINI 3 pro NO CARGA, control mini 2, control mavic 3, air 2, REPAIR CONTROLLER DJI - YouTube
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Some are saying to leave it on charge for 24 hours and then leave it a day
I mean OK worth a try but why would that work? it seems really odd 
Yes i agree, they say its about balancing the batterys
So I opened the controller again and removed the TVS thingy. It has an overlimit resistance either way so is probably ok. Controller still dead but I left it connected for a while and noticed it was quite hot. It was consuming 1.6A. Maybe a short somewhere on the board?
(However as the new controller arrived I charged it up and then tried to charge the drone, nothing!! slight panic… then tried substituting leads, chargers etc and the Dji lead is dead, in fact it seems to be short circuit. most odd).
Anyway back on topic will take the boards out and see if anything obvious but I am no electronic wiz so it may be beyond my basic skills.
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