This mobile charger should fully charge your phone about two times when the phone is in stand-by.
When your GPS app fully discharge the phone in three hours, so with the charger capacity your phone should last nine hours.
But this service people see a ploblem with their charger.
This charger will only "dribble" charge your phone, say, it'd need the double of time as the wall charger which came with the phone.
So with this power hungry GPS app the phone wouldn't properly charged. The battery would drain despite the charger is put on the phone.
The charger wouldn't be empty. but the battery would be empty.
I have a 4400mAh mobile charger which charge my phone as fast as the wall charger with came with phone.
My hiking GPS app needs about 20%/hour of the battery.
So I don't have any problems with a 10 hours trip because my phone is charging properly
I don't know if you'd reach your 10 hours with this 4400mAh charger.
But your prospects would be better
My mobile charger: JustMobile Gum Pro.
Harry