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 a solar-supported power bank.

Available directly from RAVpower, or from Amazon for £59.99/US$79.99. On Amazon US you can also pick up the 16W version for $49.99.

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.

Available on Amazon for £52.99 or on Amazon US for $119.99.

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.

Available on Amazon for £30.99/US$$39.99 or directly from Addtop Tech.

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 Plus, while the iPhone XS can get up to 6 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.

Available on Amazon for £22.99/US$32.99.

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.

Keep in mind, it won't charge laptops like the Microsoft Surface or smartwatches and all four panels will have to be exposed to sunlight for it to start charging.

Available on Amazon for £57.99/US$59.99. You can also pick up a newer model in the US for $41.99, and in the UK there's a model that converts to a higher 63 wattage on Amazon UK.