you can record without consent if you want.
but you can be sued and pay damages if the recording goes in public/you share it with other people etc
in some countries is ilegal to record without consent.
you could replace your battery every 6 months
but make sure you get genuine one (from official service, no clue if they still sell for this model) not some shady chinese aftermarket option
the listed alternatives wont give much performance boost.
skip and wait the newer phones with bigger batteries 7000mah+ and with better new gen soc/cpu/gpu.
what is your budget?