XIAOMI PRO2 Battery - Repair 3 [Manual Balancing & Full Checkup] 

it holds its output on by default with the stock firmware ✌️ check my diy powerbank videos

@@Darieee thank you for the reply! Then the 3 wire cable that is going on the main board is just to get data about the state of the battery. I'm thinking to put a custom firmware but i don't know what's the best one, can you recommend me one and also tell me what are the benefits of having a custom firmware? Thank you.

yes they do?

heey - yea - unfortunately I found an original spare battery online .. had like 5 cycles on it and sold the one I had - mentioned everything about it in my listing, including all the videos 🔥 so - unfortunately I don't remember what came of it about 4000km ... 400 of which uphill with 2 people on the scooter at 1.4kW I guess the cells were just worn out .. although .. maybe also that BMS chip was acting fishy do you have the same issue on any of your batteries ?

Hey, I have an issue oversudden on cell #10. It goes unbalanced and 0.5-0.6V lower then the rest. Initially I fully charged the battery in the scooter, then opened and charged the cell manually to top it up to the rest of the cells. Unfortunately it didn't work. After the first cycle the same cell caused unbalance. Now I opened it again and did full cycle on the cell#10. It has 12160mAh of capacity... Not sure what is causing this. The cell appears to be fine. I will try to cycle each cell to get overall capacity per cell, and then drain it prior charging in the scooter. Any advices? Noted, the cell#10 is the last cell in the pack, hence it would be a nightmare to get it replaced.

it's a balancing circuit problem I did the manual rebalance, and the BMS started AT SOME POINT unballancing a different bank so - potentially even some firmware issue .. or I just pushed the pack at 1.2kW uphill with 2 people on the scooter for too long PS: the cells I removed from my offending back were found almost dead after idling in a box for 1 year, so - they were kind of tired

@@Darieee I did a full cycle (Charge / Discharge) of each cell. I found that the cell #10 is the healthiest among all, with average capacity, 12190 mAh. All cells are within +/- 0.5% from the mean capacity. Another observation I made is that when balancing cables are disconnected, and I was doing cycling of other cells, the cell#10 has been drained from 3.18V (after discharge to 2.8V and rest/recovery to 3.18V) to a 2.9V over a week. It seems like some issue within the BMS, causing drainage of cell#10... Any ideas? Could it be an issue of a capacitor?

Another point of information. I left scooter standing still for a week, and took a snapshot of all batteries voltage. After the week of staying idle the cell #10 lost about 0.077V, while other cells lost only 0.003 upto 0.011V max. Would it be an issue in BMS, that keeps draining slowly, like a capacitor, or it is the cell #10 got faulty? Based on my manual discharge and charge test the cell has 12100mAh capacity - the highest amount others... Very strange. I probably will bring BMS to electronic repair service to check for any faults. Otherwise no idea what could cause the issue... I run the stock firmware, and normally use it in sport mode. Charging cycle from 30-40% , and very rarely discharging to 5-10% level