Look to Quantum - they sell (or at least used to) a battery compartment with coiled lead that is meant to connect into their Quantum sealed lead acid battery pack systems. It need not be used with the packs though. Their packs are nice, but pricey for what they do.

Just connecting the correct quantum module for your flash to a sealed lead acid bettery of the correct voltage and of sufficient Ah capacity should suffice. I started with a pair of 6V 5Ah, and ap pair of 2V 5Ah making up 2 8V packs with one as live, and one as the second live unit. I charged them with an old Braun pack and head flash pack that charges its' 8V battery directly with an AC lead and built in charge reguator.

Then a Sunpak potato masher flash with a Quantum battery 2 battery pack was gifted to me, with a dead 8V SLA battery. I have bought the power plugs to make leads to charge my Metz 8V batteries, but have yet to make up the cord.