GPS tech (Garmin, Hammerhead, Wahoo, RWGPS, etc)

My phone cannot cope with rides of longer than 4 hours- battery goes flat.
So, I was after something that could last ~8 hours on one charge, and log time and position.

Sorry if this is obvious, but you could try running the phone in airplane mode to save battery. GPS is passive and any app worth it's salt will have offline map data. Both gps phones I've used have been able to handle a full day of tracking before empty.