What portable backup battery charger is considered the best?

i'm hoping use iphone bicycle gps long rides (+18 hours) , have backup battery extend use.

backup battery is...
1. relatively small , lightweight.
2. able give me additional hours iphone.
3. able charge minimum number of hours.

know won't able want, consensus here best portable backup battery iphone.

things turn off wifi , talk 2 hours extend battery life. basically, iphone on standby mode except cycling app running in background record rides.

in advance.

 

messenger bags

don't know if feasible know make messenger bags can charge phones. also, using gps on phone eat battery might able 4 hours out of full charge, if turn else off.

hope helps.

 

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