ok, the Battery is well marked.
It is made by COSLIGHT, that's not too useful. It is a 3.7 Volt 3.3 watt hour (that translates to 900 mA hour)
of type CA395249. http://www.coslightindia.in/Polymer-3rd.html
It measures 3.8mm thick and 48mm by 51.5mm, like the catalog page says. You will definitely have to solder it in.
I see a lot of stuff on sale overseas that "might" work.
I see some original repl. used on ebay in different countries. You take some chances with them too.
I see some I'd like to try, but they are 5mm thick.
I dunno. If I try one I'll post my results.