These are part of the "Fly more kit". I don't fly often, but noticed a little dark spot by the QR codes on 2 of the batteries. Anyone have any issues out of batteries like that?
if you're OCD and have a thermal imaging appliance available you can power it up and then check for hot spot to see if it coincides with the discoloration. I doubt that it is anything other than ink. (I have thermal gear so it's easy for me to suggest this quick check.)