There are three versions of the Metz clip. (Battery Holders) Look inside the handle. You see three pins but your module only has two contacts.  Thus eliminating all BS and those who say it doesn’t matter, it does. For me the modules serve one purpose, to be disassembled and rebuilt as a power cord, otherwise useless.  

The modules all come from overseas, the true Metz Alkali from Germany about $28.00 for one, the TYPE three very expensive, and the knockoffs made by SONIA BRAND from Karnataka, India about three for 25.00 dollars.  Every five of the cheapie’s I use, I throw one away, poor fit, won’t lock in the handle, thin plastic.  

The first module is the older-welded cells factory issued NiCad pack.  It is welded, not soldered.  Solders are homemade refills. Also look for corrosion, not a good choice, thus good for a pack when I gut it.

TYPE 2 - MODEL 5312   45-39  METZ and SONIA BRAND
The second, type is simply an unfilled empty holder you fill, with ALKALI only, not rechargeable batteries, it is designed to work with the ground and PIN A which is in a different location from the Ni-Cad/NiMH  pack and it is the 9.X volt version. 

The third version is the newer Ni-MH offered by B&H and more current, marked new, when? How long has it been current on their shelves. Which is why I have an expensive load tester on my bench. Most likely it is what they call  “Old new inventory”  Pass if you are smart. Waste of money. NiMH has a one to two tear life expectancy when not used.

I can convert all of these holders to a battery pack module by rebuilding the unit and we’ll save you about sixty dollars.

REALLY CHEAP BACKUP, BUT - Some have tried using Sanyo Eneloops in the 45-39 battery holder, and it might make a good backup when a pack is not needed.  Recycle times are relatively better than alkalines. But you do have to convert the pack to the 7.4 side if you use the SONIA’s.   Eneloops cells won’t discharge by themselves like normal rechargeable do. Unfortunately, the cells are expensive and you must use the same cells from one batch.  If you mismatch cells especially rechargeable’s you might have a first hand encounter with thermal runaway, which is said to be an unpleasant experience.

To increase the life of your cells, you might want to use an "intelligent" charger that monitors each cell individually. One good entry-level model is the La Crosse BC-700, which can be had for less than 30 dollars US on Amazon