I have usually always a so called Powerbank
with me, a small device that you can use to recharge your mobile phone on the road if need arises. They are small and cheap, fitting in to your pocket and costing anything between 10 and 30 Euros.
I lost my old one Sunday two weeks ago when it was stolen. As it has saved my a** a few times I knew I need to get a new one. Got it this Monday, €19 and 4000mAh capacity, exactly twice that of the battery capacity of my Nokia Lumia phone.
Today after a small bet we decided to test my Powerbank. One iPhone 4S
(1,430mAh battery) 30% battery left, and my Lumia
(2,000mAh) showing 21%. Powerbank fully charged (4,000mAh).
OK, it took quite long but after a bit under 2 hours the iPhone showed 90%, thereafter my Lumia needed 2.5 hours to show 99%. All this with a Powerbank small enough to fit your shirt pocket (see image below showing the Powerbank connected to my Lumia phone).
When both of our phones were charged and Powerbank connected to bartender's Samsung Galaxy, it started immediately charge it so there was enough juice to get one more dead battery alive again.
I wholeheartedly recommend a Powerbank emergency charger to everyone using a mobile device
. Most of them come with different adapters for different connections, check the details before buying one to see if it can be connected to your phone / tablet / game.