Don’t Pass on Pass-Through Charging!

We’ve been promoting the concept of pass-through charging since the early days of portable solar equipment. Primarily with the onset of lithium battery packs. Lately, I’ve seen a lot of buzz about it, which thankfully means that the functionality is now a sought-after feature, and people understand the convenience it provides.

If you aren’t familiar with the concept, it is simply this: pass-through charging is the ability of a battery pack to ‘be charged’ at the same time that it ‘provides charge’.

Essentially, most battery packs you find at the local hardware store, or big box electronics store, can either be charging from a source (wall, USB port, solar panel, etc), or providing power to your device, but not both at the same time. As soon as you plug your iPhone into that expansion battery pack, the expansion battery pack will stop charging itself from the wall & prioritize providing power to your iPhone. But what do you do if you drained the expansion battery pack? You have to wait until it has enough charge stored before you plug in your iPhone.

Imagine for a moment you are out on a wilderness trek. You have a folding solar panel on your backpack, and a solar storage battery to capture all the power. If your camera battery, drone battery, or satellite phone battery suddenly needs to be charged, do you want to take a time-out from solar charging in order to charge your device? Or would you rather be able to keep solar charging, while you charge your device? Have all that solar power flow through to whatever battery in the chain needs the electrons? Of course you would.
So, you need a solar storage battery with pass-through charging capability.

How To Find Pass-Through Battery Packs

Most solar storage batteries offer pass-through charging. It’s the nature of the application. When you don’t know how much power is going to be flowing from the source (solar), or when you will need to connect devices for charging (loads), solar storage batteries must provide that flexibility. It follows the basic design of residential off-grid solar systems. Imagine the inconvenience if you had to unplug from solar to be able to run your fridge at your cabin? Not likely.

So, trust that battery packs from major solar manufacturers offer pass-through. This includes all the USB & universal battery packs on Modern Outpost including Goal Zero, Voltaic Systems, Random Order, EcoXGear, Enerplex, and others. Because if the company doesn’t say it’s pass-through, it won’t be.

Are All Pass-Through Battery Packs The Same?

No. Some battery packs prioritize the charging process and delivery of power to loads a little differently. For the most part, you will be storing & using all the power you generate from solar down the battery chain, but there are a few features you should be aware of…


Some battery packs will disconnect the load momentarily when they lose power from the source. Unplug the solar storage battery from your solar panel, and it will turn off its output port too, and then reconnect it a few seconds later. This is not usually a problem for smart phones and tablets that are designed to reconnect themselves to a source, but it could be a problem for battery chargers and other less sophisticated devices. They may need to be unplugged & reconnected in order to resume charging. Not always a convenient task.

Always On

Some battery packs offer an ‘Always On’ feature. This means that the battery is always waiting in stand-by mode for a load device like a phone or charger to be plugged into it. Having the power available all the time is a definite must-have for many remote monitoring applications where the load devices can’t have the battery pack time-out or turn-off at any time just they don’t need power at a particular time.

We Ran Some Tests…

We took 4 of our most popular USB solar batteries, and ran a quick test using an iPad and a Samsung smartphone to confirm how they operate in a pass-through scenario…

Voltaic V15
Never blinks… always stays connected to the load, regardless of disconnection, reconnection, or low-level solar source power. Voltaic also provides an ‘always-on’ mode, in addition to a power-saving ‘time-out’ mode, so that the battery will never time-out on you if you don’t want it to. The V44 model is designed the same way.

EcoXGear EcoCharge
This small, ruggedized battery also never blinked. connections & disconnections from a source did not affect its delivery of power to the devices. Since it doesn’t have any control buttons, and only a small source power status light, it is safe to assume that it is ‘always-on’, providing power whenever a device is connected & asking for power.

Goal Zero Venture 30
This ruggedized battery remained connected to load devices regardless of what the source power was doing. ‘Always-on’ and ready to provide charge. An excellent battery pack that performed as the best should. Venture 70 is the same.

Goal Zero Flip 20
This popular battery drops the load device momentarily when the source power is disconnected. There is no control button, so the battery is ‘always-on’, and reconnects to devices & chargers automatically when they are plugged-in. An interesting note was that the Flip 20 charged at only 50% of the rate of the other battery packs in this test. The Flip 10 & Flip 30 are similarly designed.

RandomOrder 9K
This battery pack follows the same protocol as the Goal Zero Flip series. It drops the load device momentarily when the source power is disconnected. Note that this battery also has a power button, which means that it will time-out, or shut-down, if your device doesn’t need power. Press the button to reconnect.

Questions? Comments?

If you want to know more, or have any specific questions pertaining to an application you are working on, please let us know.

Leave a Reply

Your email address will not be published. Required fields are marked *

%d bloggers like this: