this is a reply letter from Minelab regarding the RNB battery (found on another forum)
Hi ****, Minelab detectors are designed to work with Minelab equipment. I’m not going to tell you that you can’t use this battery or that it won’t work, but if it should cause a problem that requires repair it will not be covered by your warranty. If I can assist with anything further please let me know. Have a great weekend!