Wondering how we ranked and scored portable chargers? First, we did tons of research and analysis, then picked the most promising products to test head-to-head. We charged all sorts of devices with these products — everything from smartphones to smartwatches. Additionally, we also measured the actual output and pushed these chargers to their limits using a digital multimeter and a dummy resistive electrical load, as well as timing how long each one took to recharge. Aside from the electrical aspects of these batteries, we also rated and judged exactly how portable these portable USB chargers are and how much easier and more convenient they can make your everyday life. We took all of the tests and grouped them into four weighted rating metrics, with our exact procedures outlined below.
For this test, we measured the total volume and the weight of each battery pack, then scored them accordingly.
While there is a slight correlation between battery pack size and performance in these two tests, we found that some packs have wildly different sizes and weights, despite having the same listed capacity.
We also rated and scored how comfortable it is to carry these products around in your pocket. We had testers walk around and sit with each battery pack in a front and back pocket on a pair of jeans, comparing how each battery pack felt side-by-side and noting if there were any particularly uncomfortable pressure points. We selected a pair of jeans with a casual fit for this test; we felt they were a good middle ground since other baggier clothing easily fits all of the power packs, and anything tighter may preclude you from carrying many of these products in your pocket.
For our capacity metric, which constitutes 30% of the final score for each portable battery pack, we conducted two separate tests. First, we wanted to test the manufacturer claims for each battery pack. Most of the products in this review had some sort of claim of each pack being able to charge certain phones a certain amount of time.
We used a Samsung Galaxy S8 as a test phone, charging it as many times as we could off of each fully-charged battery pack, and scored each product based on if it exceeded or fell short of its marketing claims.
For our second test, we compared the actual capacity to the claimed capacity of each portable charger. We measured the capacity by fully charging each product then discharging into a dummy load through a digital multimeter. This dummy load let us set the current draw to the maximum that each pack could handle, with the meter timing how long the pack had been discharging for — and handily calculating the total energy discharged for us right on the screen.
If this sounds a bit technical, it helps to know a little bit about how these products are rated. These portable power packs are rated in some number of milliamp-hours, which for those that are unfamiliar, is a measure of total energy and refers to how much power each pack can source for one hour. You can think of an amp (or ampere) as the rate at which electricity is delivered, so multiplying that by some amount of time gives you the total electrical energy delivered. An amp is quite a large amount of electrical current, so for most consumer products, we usually attach the "Milli-" prefix, denoting 1/1000 of an amp. For example, a 10,000 mAh module is theoretically rated to be able to discharge at a rate of 10,000 milliamps (or 10 amps) for one hour, or at a rate of 20,000 milliamps (or 20 amps) for 30 minutes. For reference, most modern tablets charge at a rate of 2.1-2.4 amps, so a 10,000 mAh pack should be able to charge one of these devices for almost five hours. In practice, we found this to be far from the case.
Next, we assessed how convenient each portable battery pack is to use, primarily focusing on any additional features that made them particularly easy to use.
First, we awarded points based on how many devices you can charge simultaneously on each battery pack. We also took the maximum output of each charger into account, awarding the most points to models that could handle charging multiple power-hungry devices at once, like tablets or the largest smartphones.
We then looked at any built-in features, namely built-in charging cables for various devices and if there is a built-in wall charger. We awarded the most points to battery packs with built-in lightning and micro-USB cables — sorry USB-C users, portable chargers haven't quite caught up yet.
While most of these products rely on a charging cable to replenish the battery, some of these power packs have a built-in plug to plug them right into a standard wall socket. These are by far our favorite, as they make it impossible to forget the charging cable and minimize the amount of stuff that you have to carry around with you.
Additionally, we also awarded points based on the included warranty and whether there is a built-in flashlight.
While we initially weren't sure about the usefulness of this feature, we were actually quite surprised about how handy it turned out to be.
We timed and scored how long it took to recharge each pack. This was a relatively simple set of tests, where we timed how long it took each pack to charge when it was fully depleted, using a Samsung USB power brick and the included cable or the built-in wall charger if the pack had that.
If you are interested in exactly how a specific model did or want to see which portable battery pack earned the top spot, check out our complete Portable Charger review. Alternatively, if you are looking for a more thorough explanation of how these products work, the pros and cons of different models, and what to look for when trying to pick out a new model, head on over to our Buying Advice guide for even more background information!