Power level is displayed through five blue lights, visble through the "cartridge slot" of the Genesis cover, which is a clever design choice. The first of the lights is a simple "working" light whenever the unit is connected. It is also touch-sensitive, serving as the power butto. The other four represent the remaining charge, and carry on the Sega motif by looking like the chaos emeralds of Sonic fame. Nice touch.
Accessories include a velvet drawstring pouch with a small partition for the handful of cables it comes with, one long and one short. Both are flat, red, and fit very loosely in the three connectors on the top of the unit. On more than at least one occasion, I did find that a cable had come loose during charging, which was a tad annoying. Meanwhile, other USB cables feel like a tight fit, especially my Vita's cable. It took a bit of forcing, and I was worried about snapping the connectors. There is also a small, thicker white cable, but it is a mini-USB, which neither of my devices use, so I couldn't test it.
As a rule, these batteries usually give out after about 500 charges before they begin depleting their max (Tommo's site says about 75% is the next step down). Unlike some other USB power supplies, the internal cells are not replaceable. So, when this thing goes, that's it. However, given that I've been using it about every other day, that's at least a year away. After that, I'll be upgrading my Genesis to a Saturn.