The red and blue when you press the button is "battery low". After a while, you'll get so used to really nice warmth and vapor that you won't need to check for the two lights being on -- a sudden huge drop in vapor/warmth is battery change time.
I'm not sure what happens if you maybe have a low battery and then also try to switch to a carto that perhaps is even lower resistance (so trying to draw more current), or, equally, try to change to a higher voltage -- it wouldn't hurt the PV, just not sure what the lights would show.
General comment, at least in 901/808 land, I've found using a good adapter all the time just plain works better. There's a lot of carto variability, but a good adapter tends to work well with many cartos.
(There are also not-so-good adapters. I have one Ikenvape 901/801 gold adapter that I always use with fusions, it has worked 100% of the time. I picked up a spare from a different place when ordering other things, a generally solid vendor, turns out that that adapter is blecch. Same in 901/808 adapters -- I still use the one Buzz sent me when I bought my original Infinity, it just plain works.)
