Even the highest-capacity power banks eventually run out of charge, and then you're stuck until you next reach mains power. Unless, you buy a solar charger. Harnessing power from the sun's rays, solar chargers are a useful backup to plugging into a power point.

While we haven't quite reached a level of solar to electric conversion efficiency that can let us wave goodbye to using power mains altogether, these nifty solar chargers should get you through those dreaded "critical battery level" moments, so you can move on to more important things (like reading Tech Advisor articles, of course).

Here are the best solar chargers and USB solar power banks for phones, laptops tablets and more, whether you're backpacking, camping, or just spending the weekend at a festival. Many of these solar chargers come with micro USB cables as well.

RAVPower Solar Charger 24W

RAVPower 24W Solar Panel

If the convenience of charging your phone simply through the power of daylight isn't enough to sway you, RAVPower's 24W solar panel is also half the weight of similar chargers, which is useful for backpacking, day trips or camping. It's also foldable and waterproof.

A clever feature is it's iSmart Technology, which can auto-detect the best charging currents for the device you connect to charge. It comes equipped with 3 USB charging ports and two micro-USB cables. 

Keep in mind, this charger is solar-powered only and cannot store any of the converted energy for later, unlike the solar-supported power banks mentioned in this article.

Anker PowerPort Solar Charger

Anker PowerPort Solar Charger

The 21W Anker PowerPort boasts its PowerIQ technology, which detects the fastest charging speed for your device and delivers up to 2.4 amps per port or 3 amps under direct sunlight. The mat charges up to 2 devices at the same time, though it does not store power. 

Foldable, portable and durable, this lightweight charger (it weighs less than 1lb) is made of PET polymer solar panels and polyester canvas, making it suitable for outdoor use. However, Anker does discourage users from overexposing the device to water, though some exposure is fine.

If you do run into any trouble, Anker offers an 18-month warranty. There's also the 15W Anker PowerPort Solar Lite with 2 USB ports for £39.99.

The 24W version is not available in the US, but the 15W version is from Amazon, for $39.99.

Syncwire 16W Solar Charger

Syncwire 16W Solar Charger

This 16W solar panel from Syncwire can charge two devices at a time, delivering up to 2.4A of charge per port - though it won't store any power. 

Lightweight and foldable, it also includes nylon loops and carabiners so that you can easily hang the panel while camping or hiking, with a zip pouch to store the carabiners and any charging cables. It comes with one Micro-USB cable, but you'll need to have your own Lightning or USB-C cable.

If you're looking for a little more oomph, Syncwire also sells a larger 24W three-panel model.

The Syncwire solar charger isn't currently available in the US.

Addtop Solar Charger 24,000mAh

Addtop Solar Charger 24,000mAh

The 24000mAH solar charger from Addtop comes with three panels. It promises to charge iPhone 8 eight times, and a Samsung Galaxy S8 roughly 6 times. E-reader and tablets like Kindles or iPads can get up to 4 charges.

The USB ports on this solar power bank are covered with a waterproof rubber cap, and the bank itself boasts IP67 waterproofing, which makes it all the more appealing for those who wish to use it for camping and other outdoor activities.

It has two ports, so you can charge up to two devices at once, and you also get a 12-month warranty.

Rleron 25,000mAh Solar Power Bank

Rleron 25,000mAh Solar Power Bank

This solar power bank from Rleron has the largest capacity we've see so far at 25,000mAh. You can expect up to 5 charges for a Galaxy S8, while the iPhone XS can get up to 7 charges.

The Rleron power bank has three USB outputs and two USB inputs, one Micro-USB and one Type-C. It also comes with a Micro-USB cable.

There's a useful display too, which tells you how much battery power is left.

BigBlue 28W Solar Charger

BigBlue 28W Solar Charger

The Big Blue solar charger is another direct to device charger – again, it's not a power bank, so you won't store be able to save the power for later, but it will add a bit more life to your dying phone or tablet.

This charger has a few useful features. First there's a display, which lets you know how much current it's receiving. It also has a pocket which lets you zip away your device while it's charging. Finally, while it's not waterproof, it is IPX4 water resistant which keeps it safe from splashes.

The Big Blue solar charger comes with a 24-month warranty too.