Direct power from different terminals in a series of batteries
The problems start once the battery you are tapping has gone flat.

The other batteries in the circuit may still have enough charge to push current the wrong way through the discharged battery, causing overheating, off-gasing and other damage.

Then when you come to recharge it, you have the opposite problem: in order to put current into the discharged battery, you also have to put it through the fully charged batteries.

The best solution for this is either an entirely separate battery or a suitably-rated (at least 60V on the input) buck converter.