From today, if you are an EE customer, you can get a FREE 2,600mAh power bar to charge your phone when it runs out of juice.
You simply need to text POWER to 365 (this text will cost 35p) to receive a redemption code and then pick one up from your local EE store.
The beauty of this offer is that as well as recharging the power bar yourself, you can pop in to any EE store with your empty power bar and they will replace it with a fully charged one, free of charge. Even better, there is no limit to how often you can do this.
If you are not on EE, you can join this service by paying £20.