The problem with ELMs is the type of battery no longer exists in a fresh form. Some NOS may be out there, but for the most part, they are gone. Lithium does not have the power (amperes) to properly run the ELM unless two batteries are used in parallel in the adapters. And even then they are only good for a few rolls before going soft. The 9-volt adapters seem to hold up a little better/longer. The Varta specs the OEM battery at 1,000mAh and 6 volts. (five cells). I've gone the external battery route with mine. The cameral runs off the same Quantum battery as the flash and simply plugs into the second power port. The cable is easy to make too.
I have a Quantum battery and that sounds like a good idea. Did you have to put any kind of a load on the line to the Hassy cable? On the other hand the 9 volt solution does not add more to lug about. It already is a big brick of a body.
No extra nuthin'. The 6 volt Quantum battery is just a regular off the shelf sealed lead acid battery commonly used in small UPS ans emergency lights. They are available at you local hardware or battery store for less than ten bux. I drilled a small hole in the battery cover, using a piece of broomstick cut the size of the battery, two thumb tacks, one at each end and a coiled telephone cord, made the connections. The other end has a connector available from your local Radio Store. Just watch the polarity when assembling it all.
Gun Control is like: Reducing drunk driving by making it harder for SOBER people to buy cars.