Wanted: detachable battery pack for mxr900

[oldfart]

Just bought an old MZ R900 on eBay, it was listed as not having a battery so I bought a gumstick but when it turned up the contacts look pretty corroded and it won't charge. Thought I could try the add on ones unless anyone can suggest a different solution?

[NGY]

I have an MZ-R90, that had similarly corroded battery contacts. I took the contacts off of the player, using a fine bronze bush I removed the loose particles of the oxides and the remainings of the leaked battery juice, then dipped the contacts into 5% HCl acid (regular household stuff for cleaning) for about a minute. The acid removed the remainig oxides from the copper contacts. 

Sadly, the original protective plating  was already gone, and although after this cleaning the player worked OK, the copper contacts would oxidize again when exposed to air. Therefore, to "imitate" this plating, I tinned the contacts with a soldering iron. The player thanks very much. I know this is a kind of tinkering, but postponed the useful life of the player.

(I think I took a couple of photos of this "repair", if I find them, I post them here.)

[oldfart]

Thanks very much for your suggestion and sorry it's taken so long to reply (family issues). I'll give that a go.  While all that was happening I won an eBay auction I'd forgotten I'd bid on for an mz r55. My idea was to use the dry battery case from that.  Oops, the contacts are in the right place but the connecting screw is a different size. One good thing though; the original Sony battery that came with the r55 will work the r900. Go figure.