Even before I owned a van I was a fan of portable power banks. These little bricks can be a lifesaver when you’re on the road and need to recharge one of more USB devices. On road trips they’re super convenient for keeping phones and tablets topped off. Now that I have the van and started doing YouTube videos, I’ve added a GoPro, wireless mics, and a few other accessories to the mix. In a pinch I can even recharge my laptop from one.

All of this electricity has to come from somewhere. Before heading out I’ll charge my power bank at home, use the bank to charge my phone and other devices, and then recharge the bank when I reach my destination. Having a large power station in the van and a solar panel on the roof takes away some of the fear of running out of power, but the power banks still help. If a power station is like a hundred dollar bill, having a couple of power banks in my laptop bag are like keeping a few tens and fives in my back pocket.

Power banks come in many different sizes and configurations. Power banks are measured in milliamps (mAh) and a good rule of thumb is that a modern iPhone takes around 5,000mAh to fully recharge. The smallest power bank I own is a 10,000mAh bank designed to recharge iPhones through their magnetic charging port. I have several in the 20,000mAh and 30,000mAh range, and something I’ve learned over the years is that many of the banks with 50,000mAh and 60,000mAh ratings don’t contain anywhere near those capacities. No one at Amazon is testing or regulating these things and 5-star reviews are easily bought, so if a power bank’s capacity based on its price seems too good to be true… you know the drill.

Power banks aren’t magic; they’re literally batteries that hold a charge and can charge other things. The electricity used to recharge these banks has to come from somewhere. Ideally you can charge them from a 120v outlet or even your car’s 12v power using an adapter. But what if the power bank itself had a tiny solar panel?

What a great concept! Power banks could be left on the dash of your van, or hung from a backpack while hiking, collecting energy from the sun’s rays and storing it for you to use at a later time! In practice… it doesn’t work that well.

Over the past couple of years I’ve owned two such power banks: a 36,000mAh power bank from a company named Kapurui, and a 50,000mAh power bank made by Blasoul. Both power banks have some neat features. The Kapurui is marketed for outdoor campers. The bank is waterproof, has a built in compass, and a shock-proof casing. The Blasoul comes with six built-in cables, insuring you’ll never be without a USB-A, USB-C, or Lightning cable when it’s time to charge. Both power banks have an assortment of in/out ports, and both have built-in flashlights.

And, each unit has a solar panel that covers its entire top.

On Amazon, both banks are coy when it comes to how quickly the devices can be recharged through the built-in solar panel. Dig around, and you’ll be able to put at least some of the puzzle together. On Blasoul’s Amazon page, it hints that solar charging should “only be used in emergency situations.” The Kapurui doesn’t list any specifications in regards to its solar capabilities, but we can find some numbers by digging through the unit’s manual.

Last year I received a 100w solar panel from AllPowers. Unfolded it’s the size of two large pizza boxes, and when perfectly aligned with the sun I was able to pull in about 85w. While size isn’t everything, in the world of solar panels, it kind of is. Logically there’s no way a panel just a few inches across could collect the same amount of rays from the sun. Hidden in the manual’s technical specs we find that the panel, under optimal conditions, has a maximum rating of 1.5v. Without knowing how many amps I don’t think I can perform the math, but when connected to a 5V/3A charger, the unit can take “5-9 hours” to charge. With a 1.5V it stands to reason that the solar panel would be slower, and it is, but that’s not the whole story. That maximum solar charging rate can only be obtained through perfect circumstances — that is, perfect sunlight, perfect angle, perfect temperature, and so on. There’s a lot of hem-hawing around in the manual, but hidden in one of the attached pictures on the Amazon page, we find the truth:

“Device may take weeks to charge via solar.”

Believe it or not, that might be optimistic. After completely draining my 36,000mAh Kapurui for the first time I decided to see just how long it would take to recharge by only using the solar panel. In the middle of the hot summer I placed the device outside panel side up on a table on my back patio, hoping it would recharge in a single day. When I checked at the end of the day the device had charged so little I thought it might be broken. With a week of sunny skies in the forecast (and that rainproof guarantee, just in case) I left it on the back porch, checking it daily. The device has four LED lights that show the current battery level. After a week, the second light was still flashing indicating that the battery level was somewhere between 25% and 50%.

The Blasoul dodges the question by simply stating that you should charge the unit at home, and only rely on the solar panel “in emergency situations.”

It should be noted that at least in the case of the Kapurui, the manual warns owners not to use the product in high temperatures and that it has built-in over-temperature protection, which will disable the device. It also says never to leave it inside your car, which ended my plan to leave it on my dash to charge.

Does this mean these power banks are worthless? No way! They’re still power banks that can be charged traditionally and used to charge other items. For reasons unrelated to the solar panel I returned the Kapurui (its storage capacity was nowhere near the advertised 36,000mAh) but I kept and continue to use the 50,000mAh Blasoul. I frequently use its MagSafe port, and having all those built in charging cables is super convenient. As for its solar panel, I just pretend it’s not there. If I found one at the same price or less than another brand I might pick another one up, but I would not pay extra for this “feature”.