You can trade speed for runtime, and there are more and more hi capacity packs on the market.. they weigh more, but if they fit, a pair of 8000s would get ya to almost 5 minutes, and slightly less prop and youd be getting to that point that you want to bring it in anyway. Ive seen as high as 10000 mah stuff.. doubt Id want that much weight.. a pair of 4s in parallel could get you more capacity as well, if they fit, and if the weight hit was worth it.
I too like the looks of this boat.. plan on stocking one at the shop, along with a minimono.. good stuff.
5000mah will charge in under an hour at 5 amps, they should never be completely dead anyway. You can charge alot of batteries at higher amperages but not on a middle of the road charger.