[jyl]

I missed the hydraulic hybrid thread.

Two thoughts/questions/speculations: (1) My impression is the main advantage of a hydraulic accumulator over a battery would be in power density (ability to accept or deliver a large amount of energy in a short time). Perhaps this could be solved by adding capacitors to the battery system. (2) How much room is there to improve hydraulic accumulators? They are mechanical devices, basically a piston in a chamber with a liquid on one side and a gas on the other side. There might be more room left to improve battery technology, than to improve hydraulic accumulator technology.