I just jumped on the smart trainer bandwagon. But not being able to use it away from an outlet seems like somewhat of a downside. For example last fall I'd take my 15+ year old fluid trainer and my bike to my kid's theater rehearsals and get in a 1 or 2 hr workout in the parking lot while I waited. Can't do that with most of the new smart trainers as far as I can tell. I read that the tacx neo can use the motor-brake as a generator so you don't need to be plugged in for 95% of the functionality, but most others as far as I can tell don't do much as far as the smart/interactive perspective. They just default to 100 or so watts resistance when not powered on.

I was thinking a battery power pack could be useful if it could provide the full functionality. Is this of interest to anyone else? My plan is to cobble together something from various ebay purchases and try it out on my new trainer (elite direto). But if others are interested, if it works, I could write up and post the details. All my ebay purchases are from china so it could be a month or two before I get the parts and have the time to do the tinkering.