Extra battery life for wireless speaker?

I have a Phillips Shoqbox weather resistant speaker I take on long bicycle rides. It fits into one of my bottle racks and connects via bluetooth to my iphone so I can break the long ride blues boredom with some of my favorite tunes. The battery life is about 4 hours. It charges with a standard 110 volt to USB charger. I've seen allot of small extra life battery packs at the electronics stores. They claim you can charge them up and use them to charge your USB device if extra battery life is needed. Since my riding time is anywhere from two hours to eight hours, I would like to have extra battery power for my speaker and my iphone for that matter. The only specs I see on the speaker or 5volts at 2 amps. I have to also think about size and the extra weight of the battery pack since I try to travel as lite as possible. They come in cigarette lighter size to shirt pocket size and larger.

Will these battery packs charge my speaker up and if so, what size should I get? They range from ~2400MAH on up to 7800MAH and beyond. The higher the number, the larger and heavier the unit.

Not sure.

I have this one:
http://www.amazon.de/...006FRD8QU/

It can charge my phone about 6 or so times, maybe up to 10 not sure.
Your speakers will use more as well as an iphone (i have sony xperia sports)
It has 8400mAh, its quiet small about the size of an iphone, its the minimum i recommend for charging speakers and iphone (also has 2 usb ports)

It's a trade-off between weight and convenience. Why not use bluetooth headphones instead, which are much lighter than a speaker? Other ways to save battery are
1.Reduce the volume. 2. Place speaker closer to your head.
You don't say which batteries the speaker uses, but if you can fit higher capacity batteries instead, or a second battery/set of batteries in parallel with the onboard system, they will take longer to charge, but will last longer too. A power pack for your iPhone should be physically smaller than the phone.

They actually make battery chargers that run on Bicycle power… These are mostly used to charge cell phones but it should also work with a speaker if it charges using a USB connection another idea is a solar charger will only work when the sun is out and they are kind of bulky but they do come in various portable formats Solar Backpacks ; Portable panels that can be attached to a motorcycle or possibly a bicycle…