Best Battery Banks for Lightweight Solar Panels

We just want to make sure you’re dialed, even if part of the solution doesn’t (yet) come from us.  We’ve tested battery banks for compatibility and performance, and there’s a lot of variability in the latter. Whether you’re trying to power a production shoot or a speaker, the right battery bank can make all the difference and help you maximize what you get out of your solar panel. That said, there’s a lot of nuances to finding the battery bank that will suit your solar needs.

Why get a battery bank?

Valid question. After all, whatever you’re charging already has a battery, so isn’t a battery bank just extra weight? Absolutely, if you’re only charging small devices like phones and GPS devices, you should be fine with just a panel like the Speed Goat 25W. That said, if you’re relying on only solar it’s worth making sure that you’ll have ample time during the day to charge your device.

To state the obvious, the main advantage to a battery bank is that it allows you to store power and use it at your discretion depending on what device is running low and what time of day is convenient to charge. Furthermore, if your power bank is equipped with a DC input or USB PD charging, you’ll be able to store more power in a shorter amount of time with one of our larger panels like the Danger Cat 50W or the Swamp Donkey 100W. For instance, if you take an hour long lunch break and put the Swamp Donkey out, you’d theoretically be able to charge the majority of your hand held devices from that single hour of power stored in a power bank. If you were to just charge devices during that same hour, you’d be missing out on a lot watt hours being generated because the vast majority of handheld devices can’t handle that much power input. It’s the equivalent of having great water pressure but a shower head that’s only designed for a fraction of that pressure…it’s sort of a waste.

It's also worth noting that you can set your battery bank and solar panel up in the morning, leave camp with all your devices and come home to a full battery bank ready to charge said devices.

Why should I bring a solar panel rather than just a battery bank.

Another fair question. But do you know why a knife is a better weapon than a gun in a zombie apocalypse? Knives don’t need reloading. That is, when that power bank runs out of juice it’s dead weight (pun intended). The combination of a solar panel and a battery bank allows you to reload that proverbial gun and get those zombies.

What battery bank should I get?

There’s no shortage of battery banks out there, and most are designed for residential/travel use. That is, the input charge is delivered via USB rather than having dedicated solar input ports such as an 8mm barrel connector, DC5521 or Anderson Power Poles. This in itself isn’t a deal breaker, but there are several drawbacks to using a USB port rather than a dedicated DC port for solar charging.

Despite having USB-C input, a Garmin InReach mini will charge at a maximum of 2.5 watts (5V @ 0.5A).

USB Basics

With the exception of USB PD, all USB devices operate at 5V with varying amperage to meet the devices needs in terms of watts (remember high school shop: volts x amps = watts). Any USB powered device will communicate with the solar controller on the solar panel to determine the ideal amperage for the device, which can vary from 5V @ 0.5A (2.5 watts) to 5V @ 3A (15W for USB-C non PD). Cool right? Well, sort of…while this is convenient it doesn’t always maximize the solar panel’s output. That is, the solar panel will deliver power to the device but if there’s surplus power it just goes to waste. While this may not seem like a big deal, if you have only limited opportunities to capture solar power you probably should capture all of the energy you’re generating, right?

USB-PD

PD stands for power delivery and, as you may have imagined, delivers greater amounts of power than traditional USB sources. Which is a good thing, particularly for at home charging with a stable power supply. Most newer (and nicer) power banks haver USB PD inputs, allowing them to receive up to 100W of power (20V @ 5A). Thus, you’re able to generate more power from a solar panel using a commonly available power cord, what could be better?

USB PD charging at 30 watts (~20V @ 1.5A)

USB PD Drawbacks

There’s a theme here: everything has drawbacks. First off, all USB-C cords aren’t created equal. That random USB-C to USB-C cord you grabbed might not be rated for PD input, limiting the amount of power you can generate regardless of what the solar panel is capable of producing and what the battery bank is capable of receiving. Bummer.

More devastating, however, is the way in which some batteries communicate with the solar controller. Should the battery overheat, start receiving reduced power due to a cloud or any other scenario that could occur in the backcountry, the battery may simply stop receiving a charge. They’re fickle and at times seem too smart for their own good. At best this is a pain and you can simply unplug it/plug it back in to reset it. At worst you leave it all day and come back to a battery bank that hasn't charged, despite being plugged in all day. Not ideal to say the least.

Furthermore, some battery banks will only charge at specific combinations of volts and amps, leaving a lot of power on the table so to speak. To use another analogy, it would be like a bank only taking deposits of specific amounts and always rounding down. Depositing $58? Sorry, this bank only takes deposits of multiples of $20, so you can only deposit $40 and, no, you won’t get change. Sounds like a pretty shitty bank.

Also worth noting, although irrelevant to solar charging via USB PD, is that USB PD charging can be bidirectional, depending on the devices connected via USB PD cord. That is, instead of a battery bank charging a device, it may unintentionally receive charge from a device. The most common scenario of this happening would be charging a laptop (which is capable of charging other devices) via a power bank. In this instance, the power bank drains the battery to charge itself rather than the other way around. While most power banks have a way of preventing this, it's worth being aware of.

Advantages of direct DC input

Remember those DC inputs like an 8mm barrel connector, DC5521 or Anderson Power Poles we mentioned earlier? They have one huge advantage over USB inputs: simply put, they’re dumb. They’re not trying to communicate with the device or figure out the correct combination of volts and amps…they’re just chugging along providing power (every watt of it) at whatever combination of volts and amps the panel is currently producing. To return to the bank analogy, this bank will take every dollar and cent you want to deposit. Whether that’s $0.01 or $99, it will store whatever want. Sounds like a much better bank to us. 

And maybe dumb was too harsh a term, because in reality these ports can receive more power via a solar panel than a wall plug. That’s right, given the appropriate solar setup (such as the Swamp Donkey 100W) you’re better off charging these power banks via solar even if a wall plug is available. Freakin’ magic.

Why don’t you make an SAE to USB-C connection?

If you’ve read this far (and gained any sort of understanding) you might wonder why we don’t just make a cable for SAE to USB PD connection to harness all of the panel’s output in a common plug/interface? Simply put, we’re idiots and, at some point, would likely plug a device not intended for unregulated USB PD input into the device. Since the SAE port isn’t capable of “talking” to the device, it’s simply going to deliver whatever power it’s currently generating to whatever device is plugged into it. While this is fine for power banks, if you were to plug in an inreach, speaker, phone, or any other non USB-PD device the power would be too great and you’d possibly fry the device. Whereas if you plug one of these devices into a USB PD cable into the USB-C or USB PD port on the solar panel, there will be communication between the two and the right power will be delivered to the device.

The bottom line:

Ideally get a power bank with a direct DC input that displays input/output watts. This setup will allow you to maximize your solar panel’s output and figure out what angle is generating the most power via the watt input display.

If that’s not possible get a power bank with USB PD input (and remember that a USB-C port in itself does not mean the power bank can handle USB-PD input). The Anker 737 is our favorite for USB PD charging and, in fact, was the only power bank that didn't have any of the above mentioned issues (after all, why do you think we know about said issues). 

Most importantly, test your power bank at home both with a solar panel and from the wall to get an idea of how fast it charges. In our experience, many power banks claim one input but in reality are much slower to charge both via a wall port and solar.

While we’ll stop short of saying what power banks not to get (we have a list), if you have questions about specific power banks please drop us a line here and we’ll give you our thoughts.

Happy charging.