Has your mobile phone battery gone south just when you need it? Get a Power Bank 4000mAh, it is small, easy to carry and has a built-in cable which neatly tucks away when you are not using it.
Recharge in 2 hours with a 1 amp wall charger using a mirco USB cable.
It will provide more than 500 cycles of charging - discharging and come to your rescue when you need it. Get one.