Hi Guy's,
Well thanks for all the response, some interesting views, I think that generator is probably a tad OTT but I can see the idea behind that..lol
So, just to finish off, I did eventually get the 5000mAh external pack, I've been using it now for a week and I'me really more than pleased with the results..
After a few pre-conditioning charges to get the pack up to full capacity, the pack exceeds my expectations, even with my phone's battery practically depleted I can still use strava for all of the days ride activity whilst keeping the phone switched on to track my progress, answer or make calls if need be and at the end of my ride the phone is completely charged with plenty of charge left in the pack to last all week for other sessions as well as charging my wife's phone too.. Result..
Really happy with that, for £11.49 job done and would certainly recommend it to anybody else who may be thinking of doing the same. The battery pack is small and descreet enough to slip into your jersey packet without any fuss.
I must say that this is a good active forum, always somebody comes back with a solution.
Thanks again for all your advice,
Regards Paul.