Check out BMSOne – the universal BMS – Madhacker.org. There is an Solo battery adaptor that allows use of either standard 14.8 v lipo or li ion batteries. If you don't have stock 5200 mAh lipos, you can adjust the capacity to match your batteries. Involves changing parameters but not too difficult. It might not look too pretty holding batteries in place with velcro strap but better than flying with the old 3DR batteries and having it drop out of the sky! You can also buy newly modified solo batteries or attempt in doing your own battery conversions by removing the BMS from old Solo battery and hooking up to new lipo.
This is a great forum but also check out some of the Facebook groups dedicated to Solo like Facebook Groups or Facebook Groups and there are others. A lot of the guys in this forum also follow these groups. There are detail instructions for some of the hacks and links to other websites where products are available for sale if you aren't up to attempting the mod yourself.