Sorry, hit the SUBMIT button by mistake.
Not sure where I was editing, but you should try to find a recharger for a NiMH device that uses 3 batteries (4.5V) or find a universal one on one of the links in my first post and use that.
The connector parts are an industry standard plug/jack (2-conductor Molex) that I searched for and found a few years back, but if you can find the charger, setup some wire connectors in parallel for the 4 batteries and make your own or just search on 2-conductor Molex plug and you should be able to find the matching connector.
You may be able to get the plug at a local computer store as well...they're used for hard drives, etc.
I have 4 chargers, but I keep one set (for 4 batteries at a time) at home and one in the RV (we use the RV for skiing), otherwise, I'd be willing to sell a set if I didn't need it.
Making a charger setup on your own shouldn't be too expensive or difficult, so that's the route I'd pursue...pretty simple (and inexpensive) components if you can find something cheap that charges 3 NiMHs at a time around 300Ma rate.
If you need the polarity on the connections, email me and I'll take some photos of mine...don't know if you have any electrical background, but not a difficult thing to do.
Email if any questions, I may be able to help out if these 2 posts don't make sense.
My direct email is firstname.lastname@example.org.