USB Power Banks are small, pocket sized batteries that let you charge up any USB devices when on the go. The truly portable models are under 5,000mAh and weigh around 100g.
They offer anything from a part charge top up, to multiple full charges from dead flat. Most portable chargers are fairly similar and have one to two USB ports, a power button and LED charge level lights. Some have inbuilt torches, extra cables or can charge a power hungry tablet.
The most important thing to consider is the capacity - in other words how many times they can charge your phone.
While one may be rated at 4,000mAh, thanks to inefficiencies in charging and discharging, you will see as little as 70% of the capacity or for a better model, close to 100%.
Rather than believe the manufacturers claims, we put 12 power banks through a battery of tests to find out their real world capacities.
How we tested
We used a custom power monitoring setup to measure current and voltage over time, to allow us to calculate a real world capacity.
We used a variable load to test maximum current draw and measured the time it took to charge the power banks. Charging was done with a standard 1.1A phone charger, while discharging was done at a 1.1A smartphone rate.
Measuring the power used to give a full phone charge let us calculate the maximum number of charges the unit can give. To calculate a rough charge cycle value for your own phone, divide the real world power bank capacity by 110% of your phones rated capacity.
Available in black, white, pink and blue, the PV100 measures in at just 8mm thick.
Not only is it smaller and thinner than many smartphones, it has a nice high 4,200mAh capacity. Better yet, in real world use you can access over 90% of the power (3,851mAh) and get a charge and a half for your Nexus 5 and almost 2 and half for your iPhone.
If you need to quickly recharge it, the PV100 charges at 1.5A from a tablet wall charger – though our charge times were done at the standard 1.1A.
It's also tablet friendly thanks to its 2.48 A charging current. The only thing missing for true perfection is a second USB port.
Goal Zero Guide 10 Plus Recharger
Different to the usual fare, the Guide 10 is aimed at those who need a robust yet flexible power bank solution.
Using 4 standard 2,300mAh AA NiMH batteries that output near 5v, the comparable usable power rating at 3.7v is 3,000mAh.
Better yet, almost 100% of that capacity is available and the Guide 10 can happily charge your tablet. You can pop the batteries out for use in other devices or use AAA batteries via an included adaptor.
While pricier than some, the extra versatility is very useful. For $129.98 you can get the Guide 10 with a powerful fold out solar charging kit that can charge it up in just 3 hours of full sun.
Thermaltake Luxa2 P3 Power Bank
Shipping with a snap on case for an iPhone 5, the super slim Luxa P3 is also quite powerful. The 2,500mAh battery has an excellent 2,432mAh available.
While only just enough to give many Android phones a full charge, it will top off your iPhone 5 with power to spare, or more than double your run time.
It also has enough power to charge your tablet (albeit not a full charge) and puts out up to 3.67 A - the highest out of our tests.
The sleek little unit is stylish and well-built and comes in black or silver. It comes with a Micro-USB cable and organiser, but no iPhone cable, so you need to use your existing one.
Huntkey Ezy Go Pocket Size Power Bank
While the lowest capacity power bank tested, the slim little Ezy Go still manages an impressive 1,824mAh of real-world charging.
It's enough to almost fill your iPhone or give your Android a significant boost. Impressively it can output 2.63 A so can handle your tablet, though not for too long.
It comes with a micro and mini USB multi cable, as well as a pin style plug for your old Nokia. Keep an eye out as it's often on sale for under $20, making it a bargain.
Kogan 3-in-1 Key Ring Power Bank
With a super portable key ring design, this Kogan power bank has an 800mAh capacity.
That seems tiny, but you get almost 100% of the capacity and it's enough to give your smartphone up to a half charge.
Just plug straight into a USB port to recharge and handily it also has an 8GB flash drive built in. You can also use the entire device as a USB charging cable even if it's out of power.
It comes in Android (micro-USB) or Apple flavours and included free shipping.
Jaycar Portable Power Bank with Solar Charger
Bulky but light for its size, the key feature is the solar panel – though a full charge will take two days of solid sunlight.
The two USB ports maxed out at 2.9 A and 2.87 A so you will have no issues charging your tablet.
The USB charging cable is built in so you can't lose it plus it has a LED torch and is splash proof.
Despite the high 4,000mAh rating, the efficiency is on the lower end, giving slightly more than one full charge of a Nexus 5 and two of an iPhone 5.
Kogan Ultra Slim 4000mAh Power Bank
Thin and small yet still packing a 4,000mAh battery, the Kogan manages to output a strong result with 3,586mAh, meaning almost 90% of the rated capacity is useable.
It's got a touch sensitive on/off button as well as Micro USB and Apple charge adaptors.
It was also one of the few power banks that would accept over a 1.1A charge rate, letting you charge it faster on your tablet charger. It outputted 2.2A in our testing, so will charge your power hungry tablets.
Vantec Power Gem 3500mAh Battery Bank
With a stand out, angled shell, the Power Gem looks cool while charging your devices with its 3,500mAh battery.
Around 90% capacity is available (3,134mAh), so you can get a full charge on your Nexus 5 or 2 from an iPhone.
The Vantec also has two USB ports, though they share power, so you can either charge two phones at once or a tablet.
While not the smallest, slimmest or most powerful, the Power Gem looks cool and is available in black, blue pink and white.
Comsol Power Bank Super Slim Aluminium 4000mAh
Fairly slim and portable for the size, the Comsol still has a fair heft to it. The brushed aluminium case is great, but will pick up scratches easily.
It has an excellent 96% of the 4,000mAh capacity available (3,845mAh), letting you eke out a charge and a half from your Android smartphone or 2.5 charges from an iPhone 5.
It can charge your tablet, though only has a single USB port. It's only available from Officeworks for $49, which is expensive, but does give a no questions asked returns policy.
Jaycar USB Power Bank with 2600mAh Battery
This little power bank is cheap and simple. Rated at 2,600mAh, you get 1,953mAh in real-world use – not quite enough for a full charge on a power hungry phone, though it will bring your iPhone back to 100%.
While this seems low, it's typical of this capacity unit and is designed for top ups on the go, not full charges.
It outputs 1.61 A maximum, so will fast charge you phone but won't supply enough current for most tablets. It has Mini-USB, Micro-USB and an old style Apple connector included.
Rated as having a 2,800mAh battery, the Sony also claims 7.5Wh, which would actually be a 2,000mAh battery - so there is some inflation going on there.
It has a usable capacity of 1,927mAh - a poor result for a 2,800mAh battery but an excellent one for a 2,000mAh battery.
Don't go looking to charge your tablet as it only outputs 1.61 A. Rated for 1,000 charge cycles, if you use it a lot it will probably outlast some of the cheaper models.
Swiss Mobility Powerpack 2200
No more compact than some of its higher rated competition, the Swiss Mobility Power Bank has pleasingly quality feel.
Shaped like a lighter, it has a LED torch and a single USB port. It managed an impressive 100.6% of the rated capacity - rather than being impossible this means Swiss Mobility have likely used a real world rating, not an absolute battery rating for their spec.
It can charge your tablet, though you will need an iPhone or lower capacity Android to get a full charge. We would love it if only it wasn't so expensive.