I have a Konami Teenage Mutant Ninja Turtles I & II Handelds.  

Both units seem to be working but the sound on TMNT I is a little "soft" but still can be heard.  I played TMNT II for about 15 min and got to the third level, brought be back to all the time spent playing these as a kid. Good luck trying to figure out where to "go" in TMNT I, I couldn't and gave up after a few tries, LOL.  

The battery covers do not stay on but are intact.  

*Batteries not included :)