A nice feature on the Opus is the ability to read a battery's internal resistance. Some cells purchased concurrently and "married" can still have significantly different internal resistance, and from what I understand using them together will shorten the battery(s) lifespan. When I run into this situation, they get a "divorce", and go their separate ways lol. When using mods like the Cricket, Tres Equis or HoG V2, if makes me feel better if my batteries are in a happy compatible relationship. But batteries are relatively cheap, and there is probably little danger except to the poor battery that gets "vampired". I'm still pretty ignorant about this stuff, but I did get off my butt and learn enough to hopefully keep me off the 5 o'clock news.