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. While a few of these chargers come with a micro-USB cable, you'll likely need your own USB-C cable to ensure your device can be charged.

BigBlue 28W Solar Charger

BigBlue 28W Solar Charger

The Big Blue solar charger is a direct-to-device charger: you won't be able to store the power for later like a power bank, but it will add a bit more life to your dying phone or tablet.

With an efficiency rate up to 23.5%, you can leave it out in the sun outside to charge your gadgets, or strap it to your bag on a hike. 

Big Blue's foldable charger is on the pricier side, but it has a few useful features. First, with 2 USB ports it can charge 2 devices simultaneously. It also detects the fastest charging speed for your device – mind you, that's only 3.4A at most, but you can expect a slow, yet reliable top-up.

It also has a pocket that 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.

Pick it up from Amazon for £69.99/US$61.96 (usually $69.96(

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 unlike a power bank 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.

Pick it up from Amazon for £59.99. In the US, there's a 24W option for $59.99 (usually $79.99).

Addtop Solar Charger 25,000mAh

Addtop Solar Charger 25,000mAh

The 25000mAh solar charger from Addtop comes with three panels. It promises to charge most smartphones for 8-10 times, tablets for 3-4 times.

The USB ports on this solar power bank are covered with a waterproof rubber cap, and the bank itself boasts 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.

In the UK, it's available for £39.99 on Amazon, though prices can be cheaper. In the US, customers can pick it up directly from AddTop for $49.99 (usually $56.99)

Rleron 25,000mAh Solar Power Bank

Rleron 25,000mAh Solar Power Bank

This solar power bank from Rleron has a large 25,000mAh capacity, like AddTop's but costs about £20 less at £19.99 on Amazon UK (in the US it costs $47.46 from Walmart).

Keep in mind, this option is a power bank first and the solar charging component is only really for (very slow) top ups.

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 and an integrated flashlight.