If you're comfortable with soldering, check out this site: <http://www.racescanners.com>. There's a BP 200/205 battery rebuild kit designed for the Uniden BC100XLT/BC200XLT that will also work with the PRO-35. The PRO-35 is basically the same scanner as the BC100XLT, but the battery pack is shaped a little differently, so the battery pack for the Uniden scanners won't work with the PRO-35.
BTW, the soldering procedure to replace the battery in the PRO-35 is not too difficult. Basically all you have to do is remove the screws that hold the case together, unsolder the old battery from the positive and negative terminals, and then solder in the new battery.
Looks like you just need some tabbed aa nicads (6) soldered in series (+to-) to equal 7.2v. The original was 600ma, but you certainly could put some higher capacity nicads. I don't think I'd put Nimhs in there, due to much higher charging time and heat build up.
There may be a thermal switch or someother device in the original pack when you cut it open. If its still good you could still use that to protect the pack if building your own.