Newish member here with limited knowledge of li-ion batteries. I have recently bought a Sofirn SP36 light together with 3 Sofirn 18650 batteries. For those who don’t know, this light comes with a USB-C port and an on board charger.
I am slowly wading through the main thread on this light (… First impressions …). Already I have discovered two differing views - one group thinks this set-up is very user friendly whereas the second group think that relying on an internal charger is not such a good idea.
This second group think that risks include the 3 batteries going out of balance and much worse that one of the three may fail and still the charger will give it current. There are other potential problems but my question concerns the issue of keeping the cells in balance.
I have an aging (2014) Nitecore charger. The model is the D4 and it has a useful display showing the status of up to 4 batteries as they charge. It accepts AAA, AA & 18650’s.
Finally my question ! - Does this sound a sensible strategy for using the light ?
When the light becomes say 60% discharged I charge it fully using the USB socket and keep a record each time. After 10 charging cycles I will run the batteries down to the point where the light starts to complain of low voltage (I don’t know how it does this yet). I will then remove the batteries and charge them in the Nitecore charger. I could even do this for the next charge before reverting to another cycle of 10 internal charges.
Does this have any merits - will the Nitecore re-balance the 3 cells if they do end up unbalanced ?
Whatever you do, buy cells from a reputable dealer, buy known cells from the Big 5 cell makers—to whit—Sanyo-Panasonic, Sony (Murata,) Samsung and LG, buy the same batch code and keep them married to the specific light in question.
If you don’t already own a capable DMM, get one. Your D4 should be fine for charging duties; however, trust but verify.
The SP36 carries the batteries in parallel, they balance between them.
Following the advice of ChrisGarrett, especially use the same batch code and keep them married, will not have problems.
“After 10 charging cycles I will run the batteries down to the point where the light starts to complain of low voltage (I don’t know how it does this yet). I will then remove the batteries and charge them in the Nitecore charger.”
Question, this isn’t ever required for Li-ions in general or for “balancing” batteries in parallel, correct? I could see the logic of popping them into an external charger periodically to confirm they are charging/discharging at an even rate, but I didn’t think Li-ions ever required a deep discharge cycle (and that it was in fact bad for overall cycle life).
If in parallel, not required. Certainly won’t hurt and it’s good to check cell state occasionally.
If in series, I’d consider your method critical.
FWIW I converted a drill from NiCad to Li-on. First attempt I simply soldered a 4S series pack together with a charging pig-tail. Used it for a couple years. Opened it up to check and all the cells and they were still in balance. I was actually surprised.
Now when I do a conversion I add a balance tap and charge them with a hobby charger to guarantee the pack stays balanced. Don’t have to worry about it that way.
