Road Angel 7000 battery

As the title says, I have a Road Angel 7000. The internal battery is now useless and I want to replace it. I have taken the unit to pieces and it would appear that the battery fully charged is 4.2v and discharged at 3.7v.
I can’t find any batteries anywhere that will do this job. I can get the exact size but only in a 3.7v which is what everything uses these days.

Has anyone got any ideas?

Hi
Did you ever get any further with your RA7000 as my battery is dying now?