Most tech start-ups in the field of mobile phone battery preservation are looking at innovative ways to charge people’s phones. From the Donor Cable - a bracelet that siphons power from another phone, to trousers that charge your phone as you walk, developers are trying to push things forward; to the point where prototypes are charging using ambient noise.

But for every inventor there’s a businessman and businessmen find solutions too; only these solutions often take a more direct, lucrative route to fixing problems. A new service called Doblet plans to place portable battery packs in popular bars and restaurants, with users paying to use them. By paying a flat annual fee of $30, members can walk into any venue that stocks Doblets and recharge their phone. Those who aren't members can pay $3 for a single charge. Members can find the nearest Doblet through the companion app.

Not only is this likely to be a money-spinner for Doblet but bars and restaurants can also use the service to attract passing trade for themselves.