Far enough down the threat model rabbit hole the real solution is just ditch the phone if you're doing anything mildly antigovernment. That at least forces them to do a bit more work to spy on you.
That's always one of the big issues in opsec/security discussions, we can always imagine a more motivated or well funded attacker but the likelihood of those being deployed against you change with the difficulty of implementing those methods.
Of course this applies whether it appears to have a removable "battery" or not.