Yeah... I'm probably wasting my time. I've got 2 good batteries. Just thought I might be able to bring the other 2 back to life after watching a video. No big deal.The problem you face is likely to be that the battery's control board, ( BMS ) has disconnected the charging terminals from the actual cells, if so external charge can not reach the cells.
Even opening the battery's case and charging the cells directly is no solution, the BMS needs to be reset.
I face a similar problem with an M2P battery I left too long, grrr.
Have a read of DJI Battery Killer repairing tool
I have just tried that but it isn't working for me (((((((
The above said, there is risk in this, the battery cells may be damaged so if you manage to resuscitate the battery I wouldn't trust the battery before you put it through several full usage low hovers over a soft landing site. and even if it 'passes' I would still be wary of the battery.
There is a Chinese lithium battery manufacturer named 'HSBATT' that lists on AliExpress. They make the multi-cell OEM battery packs plus BMS board for most of the older DJI drones. I've used their products, which for me have been faultless, and have no hesitation in recommending them (if you can track 'em down).The problem you face is likely to be that the battery's control board, ( BMS ) has disconnected the charging terminals from the actual cells, if so external charge can not reach the cells.
Even opening the battery's case and charging the cells directly is no solution, the BMS needs to be reset.
I face a similar problem with an M2P battery I left too long, grrr.
Have a read of DJI Battery Killer repairing tool
I have just tried that but it isn't working for me (((((((
The above said, there is risk in this, the battery cells may be damaged so if you manage to resuscitate the battery I wouldn't trust the battery before you put it through several full usage low hovers over a soft landing site. and even if it 'passes' I would still be wary of the battery.