Hello,
I still have my PRO 43, which I bought new, and I only use NiMh batteries in it. I have never charged any batteries in the scanner, even though I have the AC adapter for it. I always have used an external battery charger.
I had one way back when that would charge six NiCd batteries at once (long gone).
You could use a MaHa MHC-777Plus-II (universal) (about $68.97) to charge them in one of the RS Battery holders, or better yet get a MaHa MHC801-D (8AA Batteries at once) (about $69.97). I use two MH-C401FS chargers. (4 AA batteries each) (about $34.97 each)
The PRO 43 was a great scanner for the time that it was made, and is still a great scanner now.
I have observed that battery life is almost linear to battery capacity. As an example, 600 mah (NiCd) batteries lasted about 6 hours per charge, and 2300 mah (NiMh) batteries last about 23 hours per charge.
Mark