A year ago, I purchased a Current C124. The first few of these scooters used Thunderskys, but changed over to GBS LiMnFePO4 cells - which my scooter is equipped with. The switch over to GBS was supposedly because of better performance, but I suspect another reason is because their supplier, Elite Power Solutions, discontinued selling the "thundersky" cells - actually Thundersky Ningbo. I had some experience with unsatisfactory performance (internal resistance way too high), which I don't see with the current Thundersky incarnation, Winston cells, but that is another subject.
The cells are mounted turned on their narrow sides. This should be OK, as these are not "flooded" cells. Only a small amount, if any, non-absorbed electrolyte is in them. The performance had been satisfactory until last month, when one cell simply refused to come to full charge voltage. Current sent a new cell which I installed. There were no visible defects, but the bad cell seemed to be lighter in weight than the other cells. It was a few days later that I just happened to press down on the safety-vent cap and discovered it was not snug against its seat - and I detected the sweet-alcoholic smell of the volatile electrolyte (dimethyl carbonate). Then a few days later, another cell started acting the same way. There was a delay getting a new cell shipped to me, and I kept riding the scooter - and the cell's maximum charged voltage continued to fall. Then, upon arriving home from a trip on some rough roads this afternoon, I discovered that voltage of this cell had gone to near-zero. I plugged in the charger, noticed some electrolyte smell, unplugged the charger, disassembling some bodywork and removed the cell cover - which revealed the safety-vent cap was completely off.
This experience confirmed what I suspected. GBS cells only rely only on some plug-friction to keep the safety valve's rubber seat sealed. There is no spring to keep the valve seated like other cells I've seen. This is a very poor design. I see no way that such a "friction-plug" vent is NOT going to become unseated from temperature change, elevation change, and especially mechanical vibration - particularly if the cell is mounted on its side. This will allow the electrolyte to evaporate and moisture to enter the cell - ruining it.
Now, the possibly is that what I actually experienced was the valves performing as they should from some kind of abusive event that heated the cell up. This is what Current may offer as an explanation - but I know of nothing that could have done this the cells have not been over charged or over discharged. They are charged at a just 8 amps, and discharged at no more than 3C or so.
Ideas? Anyone else have experience with GBS cells?