I have been able to stuff and I mean stuff Airwire receiver's, P5 sound boards, Speakers, Li-Ion Batteries all into the tender of the MMI K-27 and a PSC K-28. The K-28 was easier, since the brass tender was thinner and overall much longer than the K-27. I had to cut the Airwire board in have and use a connecting cable. Both have a false coal load over the Batteries. Both can run for quite a while, but until I start doing an indoor layout, I don't have exact run times. I use Airwire on my 1:20 scale K-28's so I like have one control system for all my engines, either the 1:20.3 size or the On3 size. I will see about some pictures later.