One carrier group of 4 cells were all sitting around 4.0 volts for 16.0 volts total… all good.
The other carrier group had one cell at about 4.1 volts, one cell at 3.45v and two cells over 4.2v! Apparently the 3.45 volt cell was self discharging and as its voltage dropped it was drawing current from the carrier with the good set (higher voltage) and overcharging some good cells! As FlashPilot said, the 4S2P config can cause other issues.
The self discharging cell is going to recycling.
These 8 cells were bought with the GT and only used in the GT… always in the same groups of 4 in the same carriers. Name brand cells shouldn’t do this… even if they are a few years old. These cells were never abused, over discharged, or overcharged.
It’s possible that the batch of cells that Lumintop got for the BLF GT had a higher failure rate than usual, or something of that sort.
It’s why I prefer to get matched cells from battery-specific stores like liionwholesale or 18650batterystore. Less intermediaries for badly matched cells to end up together.
Thats exactly what was happening to mine FBsLights. I would take out the bad one, put a brand new 30Q in, and a few months later the same thing would happen to another cell.
Im glad people read my reply and will rethink how they store their multi celled lights. I hope we can all periodically measure individual cell voltages to minimize the chances of catastrophe. Its also important to note that multi cell lights with cells in parallel are not immune to having a bad cell run down the rest. Its happened to me more than once while using"coke can" style lights and my LT1 lantern.
For me, the easiest way to spot weak cells is to charge several and then let them sit for 2-3 days before use. The gremlin cells will drop voltage as they sit, while the good ones will level off and maintain a similar voltage within .01-.02V of each other (assuming they all terminated at the same voltage from the charger).
As an aside, the Lumintop GT4/GT94 uses a single 8 x 186850 carrier with an MCPCB conductor plate sandwiched between the 2 groups of 4 cells. That plate was reported to be problematic and creates cell voltage imbalances… not good at all for a light running 4 x power hungry emitters! Removing the plate resolves the voltage imbalance problem.
Im glad you posted this to the forum. I thought about it a few times but it slipped my mind. Now we can all be aware of the potential battery gremlins that are waiting to ruin our day.
I found this thread through google. I decided to charge my BLF GT batteries today and found a similar thing to you. In one carrier I had 4 cells at 3.6v. I charged them all at once, and for some reason one of them took way more Mah to charge back up to full.
In the other carrier I had 3 cells at 3.6v and 1 cell at 2.8v.
Charing them all up now, but it sounds like from the advice in this thread I should be tossing the odd ones out and finding 8 fresh new cells. Bummer. I had a BLF GT from the initial group buy run.
Good for you! At least you actually checked your cell voltages, found this thread and were able to apply what you learned from it. You can still use those cells with other lights and recycle the “cookers” (ones that take forever to reach end of charge/terminate).
IMO, if you arent going to use your GT for more than a month, its best to remove the cells and store them in a cool dry place at storage voltage (I store all my cells @3.67V and attempt to use them in a rotation). If you feel compelled to keep the cells in the light long term, its VERY good practice to remove them periodically and measure each cells voltage, just as you have done.
