I just picked up an old Metz 45 Ct 1 on ebay, along with a couple of NiCad packs - factoring in the price of the batteries, and charger it was basically a free flash.

It all arrived, and of course I wanted to test it asap, so I put the batteries on charge, and borrowed some batteries from my girlfriend's 45 Ct 4. All worked well (with both NiCd and regular batteries) - reasonable charing times, and plausable metering.

Later that day... my batteries are charged, so I put them in the flash, and nothing happens -D'oh. Must be dead - fair enough they were old and cheap. Just to be sure I measure the voltage - they're both giving out 9volts (as they should be). Then I try my batteries in the Ct4 - they work fine.

To recap:
Ct1 + borrowed batteries = good
Ct4 + borrowed batteries = good
Ct4 + my batteries = good
Ct1 + my batteries = bad.

in other words, by a process of elimation everything works individually, but my batteries don't work with my flash!!!!

Any ideas?