The Swiss army knife may have been usurped by the smartphone as the take-everywhere gadget for most people, but manufacturer Wenger isn’t taking the change lying down.

Recognising that electronic devices aren’t much use with a flat battery, Wenger has launched a range of portable solar chargers that roll up when not in use.

The chargers are available in three sizes: the Standard with 2.25W power output, the Top with 4.5W and the Pro with 6.75W.

Each model uses an array of polycrystalline solar panels and a high-capacity battery (2200mAh on the Standard, 5000mAh on the Top and Pro) with a USB port output stores power for when gadget recharging is required.

Wenger reckons that in good sunlight, a smartphone can be full recharged in anything from four hours to 90 minutes, depending on the model.

The solar chargers are available online at the Wenger site, with prices starting from $180 (around £115).