You might want to try just the map if you have the 5s. I learned this weekend over in IM Switzerland that if you preload the map (look at the map in all the areas that you ride) that you don't need any cell or internet signal. I preloaded most of the country and went on an 8 hour road trip and the map/gps worked fine with turn by turn. Might help your battery issue considerably.

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Badig| Strava

You can also get an external battery pack. Some are quite small, but can still hold another charge or two.

Do not wait till the battery is low to plug it in. If you are losing 30% an hour, even the high-current batteries will struggle to keep up with that drain.

Yeah, Google & Apple Maps apps are quite good at offline mapping, but AFAIK they don't support navigation of a predefined route. When riding long, new routes a navigation based on predefined route would be quite useful.

I've used Endomondo and mapmyride with pretty good results, but neither does exactly what you're asking for. With Endomondo I can usually get 3+ hours in navigation mode on my iPhone 4 with ios6.