Safety wise, doesn't appear to be an issue as we are not looking at any different volatages, etc. The charger itself has protection that would keep it from overheating. I charge at the lowest setting, as it is technically off label use - however - it appears that the only reason that the VP1 isn't a 26650 charger is so that they can sell OTHER chargers for 26650 batteries.
Would I slap a 26650 in it at 1.0A charge and leave the house or go to sleep - nope - but I don't do that with ANY battery.
With the 26650, I run it at .5A and there is no indication of any problem at all. Electrically - there isn't any reason at all that it shouldn't work perfectly.
Looking at websites - looks like a lot of folks are using chargers for things that they aren't supposed to charge. No references found for the VP1 - but these sites are showing all sorts of chargers being used for 26650 even though they are not supported and..don't fit right. Basically - as long as only 1 positive contact and 1 negative contact can touch the battery - it should be just fine.
From a battery only standpoint - the only difference between 18650 and 26650 are size and capacity - the voltage and technology are the same - and they use the exact same charging algorithm.
A also have an Xtar wp6 charger - and they are commonly used for 26650.
With all that said - guess it comes down to "how do you feel about it" - I'm comfortable as I don't let my batteries charge when I'm not around and I don't feel that it is any more dangerous at all than charging an 18650 - they are, to the charger, the same thing. The charger monitors the battery regardless of what size it is. Only thing is - it can take a long time to charge a 26650 because I don't push it higher (not because of safety, I just like to slow charge batteries).
Xtar would be happy to sell you another charger that is labelled for 26650 - is it necessary....I don't think so. I will follow up if anything explodes or catches on fire
But, should we? I don't know? The instructions say 18XXX's. Is it safe?
