meehaja – I run a phone with GPS off (HTC Desire) and Bluetooth on, so lasts about 48 hours, and a very small (guess 25 grams?) Holux 1200 (about £25 on Ebay from China). The Holux lasts about 12 hours, is a GPS and sends the signal to the phone. Works well.
Uploading from my Garmin here, use both. Endomondo I prefer as a general fitness tracker/record, Strava only seems better on the segment scoreboard, the interface can be a pain to get around compared to Endo.