Can FBS rechargables be re-done?

You can rebuild it yourself and still use the factory charger...I went with 2200 mAh AA rechargeables from Harbor Freight. The battery pack will now run a Explorer for at least 18 hours on a charge...for a cost of $12! Be careful popping the case apart from the sides, hot melt glue was used in spots, so pry slowly and carefully...cut the tabs on the one end of the old AA pack close to the battery, leaving the tabs as your new contacts on that end. Dig in a drawer for a old t/v, cable or satellite remote that used parallel AA's...you've got one somewhere bust it apart for the contact spring set, stretch out the 2nd spring, then place it into the other end of the FBS pack and add your batteries as shown. Don't reverse the polarity! Snap the case back together and it's done, no soldering required...

I have never done.
Have RNB battery.

See where some folks do rebuild.

You can call batterie plus and asked.
https://www.batteriesplus.com/t/services/tech-center

I've gone to RNB on my excals but I had Battery Plus rebuild my sovereign batteries.

I'm pretty sure they can do it.