Draw 1 batt at a time, swap it endlessly. Brilliant!

I already have the other model from Watson similar to this one, that it draws power simultaneously from battery A + B which gave the purpose of DOUBLING the power making a 50 watt-hour battery turn into a 100watt. Now, the UPS one, as you obviously already read the specifications, it features a UPS (uninterrupted power supply) which has the purpose of drawing ONE (1)  battery while the other remains untouched, fully charged, ready to go on standby.  With this accessory, for example, a 50 watt-hour Micro V Mount battery will STILL be a 50 watt, BUT, with the ability to swap batteries indefinitely, one at the time, as long as you need. All you have to do is observe when that red LED light from bank B turns on, which tells you it’s time to swap the old one from bank A.  Additionally, what’s great about its intelligent circuitry is that it detects when that battery is about to run out, but without completely draining that battery to zero, which is not a good thing for the battery. So every time it’s time to change that battery, I know my costly sweet battery didn’t get over discharged, just the proper and adequate discharge rate. I’d recommend that you try getting both options as you’ll never know when you’ll need  or the other model as well. The MAIN point of buying this, is that it will give you the ability to extend runtime with your light that has only ONE V Mount plate, acting like if it had two plates which again, allows you to run your light longer. Not only lights, but ANYTHING in your camera rig that you need more stamina/ run time beyond what a single V Mount port can do on its own.. These things just work in perfect harmony with the entire Watson system and I have been using them since their first introduction.  Additionally, this device features three D-Tap ports, to even power other devices depending where and how you are utilizing this adapter. I used it on several lights that only feature ONE V-Mount plate, and this adapter gives me twice the run if I only had 1 battery installed.  Very useful for long runs.  [I have received this product in exchange for my honest review]