There’s a battle being waged beneath the surface of our electronic devices. On the one side, faster devices and larger screens consume more power; while on the other side, improved circuit design uses power more efficiently and improved battery technology stores more power in less weight and space.
The wins and losses of this battle are reflected in the battery life our devices offer us. It is hard to say which side is winning, although the last few years have seen no significant improvement in the net life we get from our portable devices.
For sure, the bad old days of briefcase sized ‘portable’ phones with battery lives of only a very few hours are happily long since vanquished, but the longer battery life offered by modern devices is still much less than we’d ideally like. We sometimes struggle to get through a single day of usage with key devices, and if we’re ‘on the go’ for much of the day, we might find ourselves staring anxiously at the battery level display and curtailing our use of the device for fear of it dying on us when we most need it.
Until the next breakthrough in battery technology (not expected any time soon, alas – battery technology is currently a ‘mature’ technology offering primarily small improvements rather than massive boosts) we have to seek workarounds to give us extra power when needed. Fortunately, there’s an increasingly effective solution and safety net that you should adopt – having an external battery/recharger device that can top-up our devices if we’re approaching a power crisis point.
This was relatively easy when all we had was a moderately low powered standard phone, where just a little bit of extra power would revive it and give many more hours of talk time and tens of hours more standby time. But now with our smart phones, transferring the power from, eg, a single AA battery doesn’t really do much.
A regular alkaline AA battery holds about 3 Watt hours of power, and can probably only transfer about 2 Watt hours into another electronic device. An iPhone’s battery holds almost exactly 6 Watt hours of power, or about as much as three regular AA batteries for a single phone charge.
The need for power is even greater with tablets. A power-hungry large tablet such as an iPad 4 has a 43 Watt hour capacity battery – it would use more than a dozen and a half AA batteries to recharge itself. That’s a lot of batteries to carry in your pocket, and also an appreciable cost for a single charge, and one can only guess at how long the charging process might take.
So we’ve seen a new category of product appear – external Lithium-ion batteries used as a rechargeable emergency power source for your electronics. If your device is getting low, you simply connect up the external battery for a top-up charge, something you can conveniently do while in someone else’s office, or while on a plane, or pretty much anywhere that doesn’t allow for connecting your wall charger and cable to the device. The devices are reasonably compact and more or less pocket-sized.
Over the last few years, they have been steadily increasing in capacity, and these days offer considerable power storage and convenient recharging capabilities, all in an acceptably portable size and weight.
Things to Look For in an External Battery
There are a number of attributes to consider when choosing an external battery.
Power Storage Capacity
The first is how much power it can store. This might be measured in either (milli)Watt hours or (milli)Amp hours. There are 1,000 milli-units in one regular unit.
Usually (assuming a notional 3.7V battery being charged and a standard 5V USB type charging circuit), to convert between (milli)Amp hours and (milli)Watt hours, multiple the Amp hours by 3.7 to get Watt hours.
Note that this measurement is how much power is stored in the external battery. That is not the same as how much power can be transferred into a receiving device. There are considerable losses as the power in the external battery is first converted to a higher (or possibly lower) voltage, then sent through the charging circuit, then converted into the 3.7V power stored in the receiving battery. A best case scenario will see at least a 20% loss, and it is common to see considerably greater shortfalls (I’ve sometimes seen devices struggle to transfer as much as half their rated stored power capacity into a receiving device).
Power Transfer Rate
The next issue is how fast it can transfer its power to a receiving device. This too is an issue that was not formerly a concern, and when the USB standard was first written, it anticipated a maximum of 0.5A of power traveling through the interface. At 3.7V, this means about 1.8 Watt hours of charge is transferred for each hour the device is connected to the external battery; so an iPhone 5S would need 3.3 hours to go from 0% to 100% charge.
That is arguably an acceptable time, but what about the iPad? It would take 24 hours to recharge it – and there’s another issue. It would actually be using up charge at twice the rate it comes in (an iPad has less than 12 hours of working life). So clearly, 0.5A quickly becomes insufficient for modern high-powered devices.
So we have seen external batteries become able to transfer power at a faster rate – first they went to 1A (great for phones, but still way too slow for iPads) and now we see the best external batteries matching their output ability to the input ability of modern devices, which tends to range from 1.5A to 2.4A.
But even a battery which could provide power at the ‘full’ 2.4A rate has become inadequate – what happens if you want to be recharging two (or three) devices simultaneously? Some external batteries now have two or even three power outputs, and can provide more than 2.4A simultaneously through their multiple outputs.
Size and Weight
These external batteries are intended to be carried conveniently, so you want one which is as light and tiny as possible, albeit simultaneously one which has as much capacity as possible.
We can’t overstress the essential importance of selecting a device which uses standard USB type connectors for both its own power input socket for when you want to recharge the battery, and for its power output sockets for your portable devices to take power from the battery.
There’s nothing more certain than sooner or later, you’ll lose any nonstandard connectors/adapters and end up with a useless paperweight as a result. You must insist on only buying devices which use fully standard connectors.
We’ve seen some poorly constructed units that have very puzzling on/off switches such that we’re never sure if they are in their on or off positions. We don’t want to have to travel with a user manual too – we want something that is foolproof and fully intuitive.
Some units come with nice little carry pouches, and sometimes with some USB cables too. That is nice, but not essential.
We’ve seen units with warranties ranging from 90 days to 18 months. While we’ve never had a unit fail in any reasonable time period, it is of course a much more comforting feeling to have a unit with an 18 month warranty alongside it, for ‘just in case’.
Another factor can sometimes be the self-discharge rate. How long does it take a fully charged unit, just sitting in your drawer, to discharge? We’ve seen some units struggle to continue indicating full charge for more than a day or two. This isn’t a real deal-breaker of an issue, but it is a nice extra thing to seek out.
Oh yes – let’s not forget about price, too! Prices of these units seem to be happily reducing – at least in terms of total capacity per dollar spent, if not in simple dollar costs.
The Anker Astro 3 External Battery
With all that as lengthy preamble, now we turn to the latest of these devices that we’ve used ourselves, the Anker Astro 3.
I really like this unit – I like it to look at, and I like it to use. And I like its great value – it costs just $40 on Amazon . Oh yes, while talking about the financial side of things, it also comes with an unusual 18 month warranty – that’s way more than most other units offer.
The unit has an all-black exterior, mainly in a rubberized material. It measures about 4.3″ x 3.2″ x 1.0″ max, and weighs 10.6 ounces.
There are four ports on one end – a micro-USB for charging it, and three regular USB ports to connect portable devices to in turn charge them.
One of the USB ports is marked as a ‘Smart’ port, the other two are called ‘Universal’. The difference is that some products – particularly Apple products – use a complicated method of ‘handshaking’ between the device and its power source to decide what speed charge to accept. Many power chargers don’t support this protocol and in such cases, Apple does not allow its device to receive power at full rated capacity (ie up to 2.4A), a limitation that can massively slow down the time it takes to transfer some urgently needed extra juice into the Apple device.
However, Anker does support this signaling and will intelligently send as much power to the Apple device as the device wishes to accept. This can halve the charge time, and also allow the device to be more protective of its own battery while accepting the fast charge.
Now for one of its really special features. Not only can it charge one device at up to 2.4A through its Smart output port, it can also charge at up to 4 Amps in total through all three of its ports in combination. So maybe you have an iPad charging at 2.4A, a smart phone at 1.0A, and an MP3 player at 0.6A, all being charged simultaneously. Or maybe there are three of you, all desperate to recharge your phones at the same time. Anker say that this device has a greater combined charge rate than any other units currently on the market.
All external batteries have some type of On/Off control to turn on their electronics, and so there is no power drain when they are not in use. The Anker battery has a very simple system – movement activates the device, and if it finds something connected to it, the Anker unit automatically starts charging. If nothing connected, it quickly switches off again.
I like the elegance of that – there’s nothing for me to remember, and no uncertainty as to if the unit is on or off.
You can tell if it is charging or not, and the state of its own internal battery’s charge, by a circular dial that has ten segments that glow white, from all ten (ie full) down to only one which in time then starts to anxiously flash quickly (ie nearly empty).
If the unit is transferring power to another device, the lighted segments slowly pulse on and off. If the unit is instead receiving power in, the segments ‘chase’ by lighting up into a full circle, then repeating, over and over.
There are no switches or other moving parts on the unit.
It comes complete with a drawstring-topped nylon protective carry pouch, and a short one foot USB to micro-USB cable that could be used either to charge devices with a micro-USB connection, or to charge the unit itself from a regular USB output source. It does not come with an external charger, but these days, most people already have plenty of these.
Note that, when choosing a device to charge the Anker battery with, choose one that has a high rather than low current output. Just about every charger shows its current output, and common values are 0.5A and 1.0A. If you have an iPad or other tablet charge, that might have a 2+ Amp output – this would be much better, allowing you to more quickly recharge up the Anker.
Using the Anker
Using the Anker is easy and straightforward. Plug something in to the unit, give it a shake, and off it goes, charging the device.
I tested it with a number of different portable devices, all of which accepted a charge from the Anker. I also did a ‘max power’ test, and confirmed it could simultaneously charge an iPad at presumably 2.4A, an Android tablet at presumably 1.5A and an iPhone at whatever was left over, and it did this without breaking a sweat (well, to be literal, it did actually warm up a little bit).
Charging the Anker unit was slower than I’d have hoped for, but when one considers it is soaking up a lot of charge, not too terrible. From dead empty up to full took almost ten hours when connected to an iPad charger that had the ability to pump up to 2A of current into it. With a 12 Ah capacity, you’d have hoped for closer to six hours to accept a full charge, but other external batteries also charge at much slower than expected rates, and slower charges are easier on the battery.
One feature I hoped to find was unfortunately not present, but it is very rare to find this on any external batteries – the ability to be simultaneously feeding power into the Anker unit at the same time you are also taking power out. This is a great feature if offered – you can be charging multiple devices with 4A of output at the same time, while still feeding in as much power as possible to the Anker simultaneously, instead of having to exclusively only charge other devices or charge the Anker. If you’re short of time and short of plugs, this feature, if offered, can be a life saver.
A definite plus is the unit’s very low self-discharge rate. I’ve had a unit sitting on my desk for a month now, and several times a day I shake it to activate it and check its charge. It continues to show all ten charge segments lit up, suggesting less than a 5% self discharge rate in a full month of standby storage. That is excellent.
I compared the Anker briefly to two other units I have here – a 4300 mAh CallPod Duo dating back to early 2010, and a Satechi 10,000 mAh unit that is still a current model.
The Callpod Duo cost about the same, for about one-third the capacity and less than one-third the charging speed, but the same sort of size and a little less weight. The Callpod Duo was a reasonably good state-of-the-art unit when I got it back in 2010 but now clearly is nothing of the sort – the last 3.5 years have seen lots of improvements. I put it back into the junk pile of products now technologically obsolete.
The Satechi unit was disappointing when I got it in early 2012. I could never get more than half its theoretical 10 Ah charge into my portable units, and it was very slow to be recharged. Amazingly, it costs more than the Anker unit ($60 compared to $40 at Amazon – probably because what was a good price back when it first came out has slowly become a less competitive price now) and can only deliver a maximum of 2A of power, making for slow difficult recharges of tablets. It weighs a little less (8.1 ounces) and is a bit smaller in size.
But who would buy the Satechi unit when the Anker unit holds more charge, transfers it more quickly, and costs less!
Update : A smaller Anker : Please see our subsequent review of the smaller Anker Astro for an alternate external battery to also consider.
The Anker Astro 3 is a well designed, well made, and very versatile and useful unit, all offered at a very fair price ($40 on Amazon).
The Anker’s 12 Ah capacity is not the highest out there, indeed, there is a 15 Ah capacity Anker unit also available, but its 4A charging rate is the fastest charging rate, and 12 Ah is probably sufficient for most purposes – almost another full charge on an iPad or more than five recharges for most smart phones. Enough for a busy day or two, or a long series of flights.