150V voltage follower
A simple solution which also has approximately matched loading at the cells is:







simulate this circuit &ndash; Schematic created using CircuitLab

The resistance seen by each cell is just over 1M and the output span of all the amplifiers is 0 to 4V where 4V is the nominal maximum for each cell at 35V. 

Given that this is a low speed application, a very cheap quad amp could be used (beware of rail to rail input devices - the 150k input resistance for output 1 amplifier can cause issues unless it is internally steered and not just overlapping input stages).