Well... it all started off with this fellow's offering:
https://www.ebay.com/itm/Rolleiflex...709619?hash=item3d1fb12af3:g:l6IAAOSwanRXh6Md . It works, and he uses 3 cells in AA form that are wired in series. Each is 3.7 volts, 2300Mah. But the charger he supplies isn't a controlled, balanced charger and mine never worked. I substituted a 12volt standard VHF radio charger I've used over many years and the charge was 1st class. I then ordered a Tenergy Balanced Charger TB6B, but in the process of learning how to use it as well as the charge tester, I fried the batteries with a short across the contacts. FWIW, looking around and watching a couple of Youtubes, seems many Balanced Chargers have the same 4-button layout and are likely built by the same folks but sold under different names. Maybe. So it likely doesn't matter much 'cause they'll almost all work the same.
Sensing that there had to be a better option, I ebayed a standard (dead) Rollei pack for the SLX with intent of rebuilding it. Didn't know I'd be doing it myself.... but Eric at Rollei USA has been struggling to find a rebuilder, so here I am and busy picking up this thread. Thanks! Bought 2 batteries that looked the same as the Turnigy Nano-Tech your photos show... and literally, the picture on Amazon was the same. The JST connectors (yellow) that they said were bought together are actually the same as offered on different sized Turnigy Nano-Techs. Turns out the connectors on this battery... which I believe are the same you have - connect the white to my balance charger's JST-XH Adapter for charging. This makes it clear that the red plug is for the discharge and to be connected to the camera through the contact plate. The Youtubes seemed to indicate that the MAh is basically the AMPs for discharge and translate on the charger to 0.8 Amps in the case of a 850Mah battery. Interestingly, the packaging for the battery and the websites (NOT Amazon's!) list the battery as 850Mah 3S 25-40C Lipo Pack, but the battery itself reads as in the photo shown as 850Mah 25-50C. Voltage on the bottom line lists as 2 cell = 7.4v, 3 cell = 11.1v, and 4 cell = 14.8v. Yet it is only the box the battery came in that we're given 3S and so 3 cells. I've seen simpler stuff in my life! but as long as we can get this thing to work... I'll be fine.
Note that the key to life in the fast lane is that Hobby King's website (HobbyKing.com :
https://hobbyking.com/en_us/turnigy-nano-tech-850mah-3s-25-40c-lipo-pack.html ) reports the discharge plug seems to be a FEMALE Mini-JST so that's what I've got to find with a red and black wire of appropriate gauge. Good news in this is that on the web page for this battery, lower down, there is a link to sale of a male pigtail to install in the battery case (
https://hobbyking.com/en_us/male-jst-battery-pigtail-12cm-length-10pcs-bag.html ). So I'll give this a shot. Worth noting is that most of the other Turnigy Nano-Techs that come up on the initial page use the larger XT60 plugs that came with my prior Amazon order as "frequently bought together"... so that decodes the mystery mistake. We could go down that road... but we won't at the moment.