I took all my 283's apart and wired phono jacks into the battery compartment. Cut the battery cover to fit the jacks. Then used lamp cord to wire connectors, a phono plug at each end. I can use any 6V battery, but I like the Gates cells "D" - 3 of them glued together and a jack wired on (that's what used to be in the quantum; I don't know what they use now). But you can get Gates D cells for about $8 apiece. And any sealed lead-acid 6v will do; the more aH, the heavier. I've used non-rechargeable lantern batteries, too. Lately, I've been using these little 1.2 aH SLA jobs I found for about $5. Got a quick/trickle charger at Radio Shack for about $10

Don't try this if you're not sure about what you're doing; the capacitor in a 283 could blow you across the room- or kill- I've seen them spot-weld a steel rod