I don't know the answer to your question, but the 18650 batteries are really inexpensive. What I'd suggest is an XTAR charger like the VP2, which shows the voltage and the state of charge of the battery so you can see yourself if the battery is self discharging and the rate.
XTAR VP2 Charger | XTAR Direct
Well, as I said, the batteries and cheap charger came with the torch.
I suppose when this battery dies I'll be looking for both a replacement and a better charger….