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 TechAdvisor articles, of course). Here are the best solar chargers and USB solar power banks for phones, laptops and backpacking.

Floureon 10000mAh Waterproof Solar Power Bank

Floureon 10000mAh Waterproof Solar Power Bank

The Floureon solar charger is a portable power bank that can store up to 10,000mAh of additional battery life for your phone or tablet...or both! With a dual USB output, it can charge up to 2 devices at the same time – though the outputs are different. One output charges at 1A, and the other at 2A, the latter recommended for tablets.

The water resistant Floureon power bank is aimed for outdoor life, with a built-in flashlight and compass. It's also dust and shock proof. It also has a 5-LED indicator to let you know how much power you have left.

Floureon recommends, like of the other solar battery packs here, that solar charging is only used for emergencies as it is slower than charging directly.

RAVPower Solar Charger 24W Solar Panel

RAVPower Solar Charger 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. 

AUKEY Solar Power Bank 12000mAh

AUKEY Solar Power Bank 12000mAh

The AUKEY Solar Power Bank offers a 12000mAh storage capacity, which is enough to charge an iPhone 7 Plus two-and-a-half times. This charger is splash-proof, and like the BSAMZ solar charger, also anti-shock and dust-proof. It comes with two USB ports and a 3.3ft Micro USB cable.

In terms of churning solar power into electric power, this bank offers a conversion rate of 23.5 percent, so if you're only using the daylight to recharge your device, it may take some time. The strength of the sunlight will also affect how fast your bank charges.

AUKEY also offers a 24-month warranty on their products.

The US version of this solar charger is slightly different, in that it also has a built in cigarette lighter and a 3 level flashlight setting.

Bernet 24000mAh Solar Charger

Bernet 24000mAh Solar Charger

With a whopping 24000mAh capacity, this solar power charger can charge an iPhone 6 nine times and a Galaxy S6 seven times. It charges up to 3 devices at once.

Like some of the other chargers on this list, it is advised to use the solar power in emergencies, only because this process takes longer. Bernet says its charger is still 1.5 times faster than traditional solar chargers, though.

Apart from an 18-month warranty, you also get a Micro USB cable and a nifty USB-powered fan (which you might as well use if you're out charging your device in the sun). 

Olebr Solar Charger Power Bank 24000mAh

Olebr Solar Charger Power Bank 24000mAh

This solar power bank from Olebr packs a formidable 24000mAh of power, which makes it ideal for juicing up depleted tablets and power intensive smart phones. The Olebr power bank promises an 8% solar to electricity conversion, so be sure to have the power bank charged before hand and use the solar feature only when you really need to.

Like the Bernet solar charger, the Olebr also has 3 USB charging ports that provide a 2A output. The Olebr also prevents over-charging, over-heating and short-circuiting, as it stops charging once the phone battery is full.

It's not available in the US, though US shoppers can find a similar solar power bank from Allsolar for $39.88 on Amazon.