A:AnswerYes but you will have to do some semi risky disassembly. The battery is completely and fully replaceable but you need to take the speaker apart (although being very simple it is still semi risky) pro tip = follow every step thoroughly. If you do that is is completely harmless to the speaker.
A:AnswerSadly no. THe jbl flip 4 has the more widely used (jbl connect +) as the jbl flip 5 has the more new (Jbl party boost) and they are not inter-compatible
A:AnswerCheck out the detailed comparison on our JBL Flip 4 and Flip 5 here:
https://www.jbl.com/compare?cid=bluetooth-speakers&pid1=JBLFLIP5BLUAM&pid2=JBLFLIP4BLKAM