I have always been a fan of battery powered locos. My dad's layout used Red Arrow and we had about 12 locos fitted out with it. It was really good, no power at all in the track just great running, at least until the batteries ran out ! I switched over to DCC at least 10 years ago, the main reason being sound, Red Arrow doesn't support it. Now I have found a battery operated DCC system, DRS by Tam Valley . Its pretty simple, you attach a small transmitter to your DCC system and place a small receiver in your loco. The receiver is battery powered and picks up the DCC commands send them to your decoder together with power. I have just installed this in a JLTRT class 37 and it works, full sound and wonderful slow speed running as their is no power interruption. As usual its not quite as simple as it sounds but it has taken me about 4 hours to install it in the loco, although I would imagine the next one will probably only take half that time. I have used 8 AAA nickel metal hydride batteries, in 2 four battery holders and run together in series to give a nominal 9.6 volts. Here they are located in the number 1 end of a 37 (ie under the fan). NiMh batteries are safe option, they are easy to charge either with a trickle charger or you can fast charge them if you want to. The Tam Valley website goes on quite a bit about using LiPo batteries but for 7 mm diesels I don't think that will be a need to use them. If you do though charging them is a lot more complicated and they can explode if you get it wrong. The trickiest bit of all this is working out how to recharge the batteries. To recharge these batteries I will flip the loco on its side and connect a crocodile clip to each of the brass screws in the fuel tank (or is it the water tank ?), you can just about make them out above. You can also see a switch that I have fitted in a slot milled in the tank, this is turn the power off when not in use. Here you can see all the bits and pieces in the loco. On the left is the receiver, as you can see its the same size as a the Loksound decoder on the right. You need to solder an aerial to this, its a piece of insulated wire 3.26 inches long. It's the thicker yellow wire in the photo. It's 3.26 inches long as that is a quarter of a wave length. The radio frequency is 869 MHz which is specifically for the EU. That is it, I have still have quite a bit of work to finish this loco off, I'm busy adding some weight to it right now, but it ran great on my test track this afternoon. I also need to add a full size speaker which I will shortly and then give a it a proper run on the layout and see how long the batteries last. With Red Arrow you would get 4 or 5 hours running time.