Bought this several years ago but never found the time to use it much. I have remembered to topped up the battery a few times a year, and it has been stored inside at room temperature, so the battery should be in good shape. One modification that I made was add some foam strips around the cartridge slot because I found that the fit was slightly loose and the cartridges could shake around... this solved that. For info on the actual device check the website link:
http://retro-bit.com/retroduo-portable-handheld-console-core-black.html
In addition to stock accessories, I'm including extras that I bought separately (no parting out, this is a bundle):
-aftermarket controllers x2
-RetroGen (allows Sega Genesis games to be played)
For the sake of search terms, I'm adding here that this plays Nintendo and Super Nintendo games.