I use a two-fish block as a bar mount. Yes, the batteries are rechargeable, the H600 lights use Li-ion 18650, the H51c uses AA (low self-discharge NiMh lights are highly recommended; Sanyo Eneloop, Maha Imedians).
This is a twofish block.
Protip: for heaver lights or to lock any bike light mount into position (sometimes handle bars and bikelight mounts do not work well together) use rubber splicing tape to hold in position.