Hello,

I hope there are some specialists here who can help me with a battery issue.

I have not used my Mini 2 for 3 months. Batteries 1 and 2 were stored inside the charging hub (not powered!) with an initial charge of about 40%. Battery 3 was stored inside the drone with an initial charge of about 60%.

Today I wanted to fly the drone and therefore I checked the status of the batteries. I noticed that pushing the button on the side of the charging hub did not cause any lights to light up (as if they were completely drained). Connecting the USB-C cable to the charger caused battery 2 to start charging normally, but battery 1 showed 4 flashing lights: 3 flashes - pause - 3 flashes - pause ... The battery inside the drone had a charge of around 50% and can be charged without problems.

4 flashing lights on the charging hub indicates a faulty battery...

I inserted the faulty battery in the drone and when checking the battery status using the on/off button it showed a blinking LED nr. 1, which I think indicates a charge lower than 25%. Connecting the chargers briefly starts the charging procedure (LED nr. 1 on, LED nr. 2 blinking), but this is immediately followed by a flashing LED nr. 4 (3 flashes - pause - 3 flashes - pause ...) again indicating a battery problem.


It is actually possible to start up the drone with the faulty battery and connect to it using the remote controller and the app. In the app I immediately see a low battery warning and a battery level of 16%. But I also see a 'battery temperature too high' message. Navigating to the battery status reveals battery voltages of 3.6V for both cells but a temperature of 192 degrees Celsius! Clearly that is incorrect, because when I take out the battery the temperature is barely higher than room temperature.

Any ideas if this can be fixed?
Somewhere I read (for Mavic Air batteries with a similar erroneous temperature problem) that draining the battery to a level below 8% will cause the battery to reset and may solve the erroneous temperature reading.
Do the Mini 2 batteries also have such a reset feature when drained below a certain percentage? Or is there another way to reset the faulty battery?

Any help is appreciated.

Hello there Herbie53. I am sorry for the trouble this has accused and thank you for reaching out. May we please know if your DJI Mini 2 is on its latest firmware and please try to drain the said DJI intelligent flight batteries and please try to recharge them for us to see if the issue will persist. Thank you.

From your description it appears that there is an open circuit in the thermistor circuit. Usually, such problems can occur after flooding with water. I am repairing the battery and I could help, but remote assistance is not possible. You have two options: use the DJI service, or send the battery to me. Greetings.

Thanks for the suggestions. I also suspected an open circuit in the NTC circuit (or a faulty NTC thermistor), but it puzzles me how this could happen since the battery has not been in contact with water or mistreated in any other way.
I live in Belgium so I guess sending the battery to Poland and back for repair will cost as much as purchasing a new one (around €54), although I appreciate the offer.
Since I have nothing to lose, my next move will be to drain the battery until it resets, speculating that maybe not the sensor circuit itself but the on-board controller has entered a faulty state.

To answer stephen: the Mini 2 is indeed on its latest firmware.

Update:

I have drained the battery further until below 8%, after which it entered self-protection state and the drone powered down automatically.

Connecting the USB cable to the drone lets the battery charge for about 2 seconds, after which all 4 leds start blinking in bursts of 3.
Putting the battery in the charging hub immediately causes the 4 leds to blink.

So resetting the battery hasn't helped.  I guess this is indeed a hardware fault in the thermistor circuit...

The reset of the BMS controller can only be done programmatically using the reset command. You cannot do this without the use of specialized software. File a claim with DJI. I am convinced that they consider it justified.

FIle a claim, batteries have a better warranty now

Thanks. I have followed your advice and contacted support. Let's see what happens next.

Why would a thermistor or any electronic component give up its electrical connections due to water?
It's more likely that if both water and voltage/current is involved, it could cause short-circuits which possibly then could destroy the electronics involved.

The main destructive factor of electronics is electrolysis as a result of the flow of current in an aqueous environment. Soldering points arranged close to one another with a potential difference are particularly susceptible to this. Practice shows that the user is responsible for most of the damage. The remaining few percent are spontaneous failures.

Update:
I have interacted with DJi after sales support.
The good thing is they respond very quickly.
Their first response was just the standard response with battery trouble-shooting instructions. Since I had already performed all those steps before my initial request, this was of course useless.
But after replying to their first response, they really read my request and their answer is:

- battery must be sent back for repair because the 4 LEDs are blinking (only to be sent back if it is not swollen).
- battery is older than 12 months (which is correct: it is 13 months old) and therefore no longer covered by the warranty. So if you send it back for repair, it is at your own expense.
- therefore we advise you to purchase a new battery form an authorized DJi-dealer.

In fact in the mean time I already purchased a new battery for €53.99.
DJi's support is correct, but it is a pity to have a high tech battery sitting on my desk that has stopped working after only 5 charging cycles and that is probably perfectly fine except for a failure in the temperature sensor circuit...

In that case, in addition to wishes from me for the holidays, see the correspondence on private.