Just to follow up on my previous post.
First of all big thanks to davidmpye for the custom firmware, this has now resolved the issue.
Here is the complete history:
1. Bought Dyson V10 in August 2021 on eBay from the official Dyson outlet as refurbished. Looked brand new without any scratches, marks, dust or dirt. I assume it was new/unused old stock just repackaged in plain packaging just to shift more units without reducing standard price or introducing big discount which could undermine RRP and future sales, and less warranty commitment. But it could have been used battery or unused battery that has been sitting for long time.
2. By August 2022 battery was only lasting about 1 minute instead of original 6 min in Max mode and we do use Max mode quite a bit. I don't know what the Low mode can be used for, Mid setting is OK when using motorised brush but for any open ended sucking without motorised brush it's useless and even in Max mode is just OK, not great.
3. So I ordered aftermarket replacement battery from eBay, this was lasting longer than used OEM battery in Mid and Low but was unusable in Max only lasting around half a minute, less than the old used OEM battery. So it was returned.
4. Opened up battery and measured voltages to see if any of cells were low but all they were pretty even so I ordered new Molicel P28A batteries to replace original P26A cells and replaced them. Replacement went OK without any issues. I did not have charger for 18650 cells at this time so they were not charged or balanced before putting in battery, they just went in as shipped.
5. Fast forward to 2025, almost 3 years later and the replacement cells are not lasting that long now as well on Max mode, so needed replacing again. I still had P28A cells from 2022 as I had to buy more that time to reach minimum order value from wholesaler, I had bought 20 cells at that time from wholesaler for less than it would cost to buy 7 cells from a low quantity/value retail seller. Since I had the cells already I used P28A, if I had to buy again I would have chosen P30B
6. This time I have the charger so I charged the cells to 100% before putting them in the pack, I assembled the pack and it does not work, just getting 20 flashes of red LED so I am thinking;
a) Dyson only charges cells to around 4.1V an me putting in cells charged to 4.2V have triggered overvoltage fault but unlikely:
b) more likely that first time replacing cells BMS was off and I did not wake up it until all cells were replaced, on the second time I may have accidentally pressed the button while changing cells and started up BMS which registered balancing error due to some cells being 4.1 or 4.2V and some cells not connected reading 0V.
5. Got myself Raspberry Pi Zero 2 W, connected 4 wires without 3.3V, tried to flash it and unsuccessful. I see Tony1s had the same issue without 3.3V so I also connected 3.3V and was successful this time. I think BMS has it's own 3.3V and it works on faster PIs, but with slower PIs, BMS times out and goes to sleep/turns off and cuts 3.3V before PI boots up and tries to flash ne firmware.
PS: When I replaced cells first time, battery was fully charged using Dyson charger and all voltages were close so I ruled out it being single rouge cell and replaced all. Second time all voltages on fully charged cells were even again 4.094-4.097V. But since now I have charger for 18650 cells, I did run some tests on them. The unused replacement P28A cells that I bought 3 years ago were 15-22 miliohms at around 30% and capacity 2530-2588mAh, the P28A cells that came out of pack were 18-26 miliohms at around 30%, 6 cells were 2100-2250 mAh on first test but one cell was only 856 mAh. I ran several additional charge/discharge cycles on that cell and it recovered to 1903 on second run and then 2066 and 2133. So I may have been OK just running some full charge/discharge cycles on the single weak cell and reusing all 7 cells that I put in almost 3 years ago.
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