I bought two of these the other day at Repco, marked down to $120 each.
http://thepowerall.com/One for the bike, one in the car. After the experience of others with them, they are handy and can always act as a big backup power source on longer rides using USB cables. Some other brands have a 16v output as well for laptops, if you need it.
I got to use it over at Lionel's places when water got into a driving light relay and turned it on, flattening the battery overnight (it was parked outside). And we need to start to the bike to test out some other things. So on it went, bike started first time, easily. So no embarrassment for me, bike worked, and battery on the FJR was charging.
Out of the case it fits under the seat of the bike. On the ST1100 should easily fit in the tail even with the McCruise module and a CB radio module.
I haven't tried it on the car yet, probably should just in case. If it starts a 5.7 V8 that will do.