Do you mean FW50 batteries? If so, it’s not normal. It could indicate a failing battery or bad charger. If it’s a good quality charger that has been trouble free until now then it’s more likely a battery problem.
Note that lithium ion batteries age more quickly if stored with a full charge, so in seasons when I’m not using the camera a lot I try to store my spare batteries partially discharged.
I never charge batteries in the camera because I feel that’s the time they are most likely to burst or burn. On the other hand, the camera’s charger is probably better quality than off brand chargers, so it might be less likely to cause them to fail.
I have been learning about L-ion batteries using them in packs to power motor on bicycle front wheel...best at less than 100 % for storing, which mostly what we do, so we have a couple to use...if we do not forget to take with.
I don't want to link to anything specific because I have never tried it. But some googling pretty readily turned up some ideas that looked like jumping the battery like you would a heart attack patient. Apparently it shocks the system back to life (maybe kind of literally).
If you don't have the equipment, I am not sure getting said equipment would be any cheaper than just buying some new batteries.