Glider radios from Europe etc

My fsg71m , the Led panel has finally died so I cannot see the freq.
None of this model is being advertised for sale at the moment so
I can do a straight plug in replacement.
Others have said the AR4201 is a good unit but I see the specs indicate
13-14 volts power supply , how does it handle 12 volt batteries or will I
have to add an extra 2 volt capacity to keep its performance.
I have seen ATR500 and ATR600 with the same power requirements.
We are required to upgrade our transponders this year to ADSB out
so budget is a consideration.
If anyone has a radio with old 25 freq spacing please send me an
email with Pic, price etc.
gfoneill AT xtra dot co dot nz