I use the extra panel battery as I like to keep an eye on the percentage or time left before recharge. It seldom loads when booting or rebooting, if I log out and then back in it then usually loads but not always. Then if I add another when I log out an in there will be two or three batteries. It has to be a bug in Mate across Debian/Ubuntu as has been the same on Parrot, Sparky, Debian, Mint, and Ubuntu Mate installations I have used. It was not always that way, it used to be stable but became unstable on a release a couple years back, but I agree, it gets very annoying.