We have this old 710 my child plays with and the battery is flat. When I plug it in I get a battery picture with a think red line at the bottom of the battery showing it's flat I guess - and we hear a buzz.
The red line doesn't get thicker. The picture flicks on and off about every second or so. The buzz comes back every couple of seconds or so. It buzzes when there's no picture. Then the screen will light up for a split second and then go off, then maybe the battery pic will come on for a second or two...
Look pretty scrambled up to me.
Anything I can do about it?
Unfortunately your Nokia Lumia 710 is now supported by Microsoft, not Nokia or HMD, since Microsoft bought the Nokia devices business (including Lumia) some years ago. For support with your phone you need to go to https://answers.microsoft.com/en-us/mobiledevices/forum/mdlumia or https://support.b2x.com/.
Good luck :)