now as some of you know i repair allot of weird electronic gear so heres a little story
attached are 2 photos, its a pair of 18650 batteries in parallel so theoretically 3.7 volts but double the current capacity as they are in parallel
Attachment 153496Attachment 153497
well my customer complained his light didnt last as long as his mates one with the same model. they both dragged the same current so i cut open the battery pack, the one at the top is a 18650 battery, what is below it is a fake battery filled with what looks like sand to make it weigh the same. since they are in parallel not series the light still works but runs out of power earlier than a proper 2 battery unit.
and this is why you always buy name brand batteries from a reputable person or company