I have just received my  DJI Osmo Mobile gimbal, and set up all worked fine yesterday.  It charged up very quickly, ie the green right on the right went on after about an hour, but I left it charging for a few in any case.  It was all working fine, and then I thought I'd put it back on charge... and left it on charge overnight... but the red light won't go off.  I put it into operation today, and it seems to work fine... but red light is solid constantly.  Isn't it supposed to turn green once fully recharged?  
I've taken the battery out, waited a minute, put it back in.  I've attempted to put the charger pin in, taken it out... I've tried to reboot, but that doesn't seem to work.  

Any suggestions on what I'm doing wrong or how to fix the problem?

Don't worry, as long as it works normally