> highest we can get away with

Assuming this means highest voltage that's still mostly safe and does not require a whole bunch of insulation, we might be looking at something from 80 to 100 VDC? No idea where I read it from but apparently it takes about that much DC voltage for people to "feel something" when touching conductors with dry skin.

A lot of industry like datacenters and vehicles are moving to 48V. 48V is right on the limit of what is considered low-voltage and therefor doesn't have special safety requirements. And because it's a multiple of 12V, it can work well with old equipment by putting exiting supplies or batteries in series, and using very efficient constant-ratio down-converters.

see for instance: https://www.vicorpower.com/documents/whitepapers/wp-boosting...