I have the pronto TSU6000 and the battery needed to be replaced. The unit always needed to be charged daily, but it got to the point of NOTHING happening. The TSU6000 takes a 4 cell NiMH battery pack. After much going to the store I could not find any 4 cell battery packs. I then went to radio Shack and purchased some 2 cell AAA battery holders. I then discovered that the battery holders would not fit into the pronto battery compartment. So I took the metal clips out of the battery holders. Took apart the original battery to see how it was constructed, and then soldered wires to the metal clips so I would still have 4 LIVE wires on the battery plug. I reused the original battery plug (where it connects to the pronto). I then glued the metal contacts into the back of the pronto (don't use hot glue for this or you'll be sorry.) Once I had the clips in place I then purchased 4 high capacity NiMH AAA rechargable batteries. The new NiMH batteries have a much greater capacity than the originals which means they last longer between charges. Since you are using the same TYPE of rechargable battery you can still recharge using the docking station. (Don't try using Nickel Cadium or LiPo batteries where NiMH are called for, as they have different charging requirements). With this type of setup you have the advantage of being able to use the docking station to recharge as well as being able to swap out with standard AAA batteries as need arrises. I have a second set of NiMH AAA batteries as stand by so I can swap batteries between charges and don't lose anything. Hope this helps.