I use the TSC Keep-Alives. It's what I started doing my installs with. So far, 90% of my installs barely have enough room for the LM, the Keep-Alive and a Speaker. There's no room for the relatively huge RailPro PBM-2! I do have one Rapido loco factory installed with their Mo'Power unit, but it barely gives me 3 seconds of power, so I'm not sure about it, but the rest of the install is working perfectly, so I'm not worrying about it!