- No need for dc-dc.
- if you use halogen bulb it is fine to made soft start (longer bulb life , possible overvoltage drive - more light )
- Li-ion could made that big lamp to much buoyant
- NiMh have more constant current discharging profile
PS:
You could mod it on HID ( because of big reflector , space , and lover temperature that produce 50W/100W halogen bulb)