I'm in the process of creating a fleet of battery locos which I can use to run my railway (at present my locos are mostly DCC). Here's where I'm up to so far:
The first battery 'loco' I built was a conversion from two Andel freelance coach kits to make a sort of railbus:
She was originally powered by an IP Engineering gearbox and motor but this wore out and so she now has an MFA gearbox motor. She has a 12v li-ion battery and a Deltang receiver/controller.
My second battery loco was built from an IP Engineering kit.
I replaced the IP Engineering gearbox with one kindly made by a fellow forum member. She is powered by 10 AA NiMh batteries and controlled with a Deltang receiver and Brian Jones Mac Five controller
My third battery loco is an 0-6-2T
She has an LGB motor block, a scratchbuilt body, 12v li-ion battery and a Deltang receiver/controller. She is by far the most reliable battery loco and the one most enjoyable to 'drive'.
And the latest addition to the line is an IP Engineering Lollypop railcar:
Presently powered by three AA alkaline cells she will shortly be powered by four AA NiMh batteries. She is controlled via a Deltang receiver/controller.
I am in the process of constructing another steam outline loco, using a Playmobil motor block. She will be based on one of the Southwold Railway Sharp Stewarts - either one of the 2-4-0Ts or the 2-4-2T.
I have another couple of LGB motor blocks which I could press into service but will hold these in reserve in case any of the present locos give up the ghost. I also have a couple of the cheap Playmobil motor blocks (with plastic wheels) which I might use to make something for the nephew and friends' kids to play with when they come to call.
It looks as if there are more and more opportunities for battery power developing - with 2.4gHz transmitters and receivers falling in price, battery technology developing (and cheapening) and miniaturisation of electronic gear.
My (albeit limited) experience suggests that either buying one of the ready-to-run locos (eg as provided by Brandbright) or adapting a track powered loco (as many others have done on here) is the most reliable approach as some of the lower priced kits can be somewhat unreliable.
Rik
Edit: Sorry the images and then some of the text kept disappearing.