While Oban notes a concern about the adequacy of batteries, I think we're jumping too quick to a gasoline solution to his problems.
As I understood it, he wants to do most of the pedaling, and only needs some assistance with the hills.
Correct me if wrong, but I think an electric solution may better fit his needs, in being less heavy and awkward when solely under pedal power.
Brenton
Well it is pretty tough to suggest any motorizing option without seeing the bike, but electric sounds perfect, especially if it's a V frame road bike gears.
SickBikeParts has a nice 36V electric shifting kit for ~$400US, and you get a pretty decent 36V 'water bottle' LI battery with mount and charger for ~$300US.
This an electric I did on a beach cruiser with an S downtube so I had to mount the 'bottle battery' on a rack in the back, but on a V frame it bolts right to the downtube bungs for a water bottle, hence their name ;-}
The motor can be mounted above or below the pedals cranks.
I put it above on this one because it was easier...
But if you have no center cavity room because you shove a 1KW 48V battery pack in there, it mounts below just as well.
Your pedal cranks and sprockets get replaced with a special sprocket pair mounted to a freewheel bearing that your pedal cranks attach to.
The motor also has a freewheel sprocket, as does your back wheel.
In short this isolates your pedals from the sprockets like a ratchet wrench.
If you pedal forward it turns the sprockets and the motor sprocket freewheels so no drag.
When you give the electric some throttle it spins the chain but the pedals don't move.
Regardless, be it your legs or the electric, or both at the same time, you get all the gears on your back wheel for both.
In short, ride around as usual with no motor help and no drag from a helper, and just give the electric enough throttle when you want to make your legs bionic.
Tough mindlessly easy and clean system for your needs to not consider as I sure like them.
