It seems like we have wrecked out two batteries because we forgot to turn the power off the computer, and it totally discharged. Any way of getting them to charge again? The cell voltages are too different for the charger.
Is it really no low voltage cut-off in the battery management system in the battery pack? Wouldnt it be an idea to implement this, or would it hurt sales
Please see this thread for some possible procedures to possibly partially recover the battery.
Note that this procedure caries a certain amount of risk, and the utmost caution should be used!
However, if in your case the cells are in fact completely dead (0 V) you should not attempt this procedure and instead safely dispose of the battery at a battery recycling center. In any case, over discharging the battery below the bare minimum of 10 V total (2.5 V per cell) will cause some degree of permanent damage, and capacity/discharge capability will be affected even if recovered.
The is no BMS or low voltage cut off system built into the battery or the BlueROV2, voltage should be monitored with the PSM and voltage display in QGC while diving to determine when the battery needs recharging. Due to the high current the BlueROV2 can draw (bursts of up to around 130-135 A) a cutoff or switch that can handle this is difficult to implement and would be expensive. We are working on this, and are developing a reasonable cost solution that will work.
The integrated protection in many 18650 cells is to prevent a fire in case of a short (cut off at too high a current), they do not cut off discharge at low voltage. Very high discharge cells like the Samsung 30Qs we use in our battery are necessary to properly power the BlueROV2.
I by mistake did over-discharge my BR 18Ah battery to 2V and it was not possible to charge it with the LIpo charger. I used a power supply and limited current to 1A and over a period of 5 hours charge it to 12V. And I monitored the balance between cells and no larger difference. After that I could charge battery with the LiPo charger without any problems. After that I have tested the capacity of the battery and it still have the original capacity of 18Ah