Thanks all - had a look through and the best on amazon seems to be powermonkey and also a Duracell USB charger. That one seems a bit cheaper as well but rated slightly less than the powermonkey.
Re borrowing another gps. I'd like to track my heart rate and my wife's garmin won't sync with my softtouch hrm and thus I don't want to wear her harder hrm version. Anyways, small details I think! Thanks for the replies though!
Had an absolute blast, did both the 10k and marathon and was blown away by the organisation and just sheer fun of it. Was my 4th marathon and although it was a few minutes slower than my others this year (3.55) feels like a huge win given the course and conditions.
BUt why am I thinking about doing it again!!! Madness I tell you!!!