I have a modern smartphone, Back in the good old days we were getting to the point where a mobile phone would stay charged for almost a week. The Problem was it was so infrequent that you might forget that it did need some juice occasionally.
Smartphones as most owners know can struggle to keep going for a whole day, and if you use them hard (Camera, GPS etc) can often drain in a matter of hours.
I find this especially when walking or sightseeing all day, using Runkeeper to track my walks and provide tracking information. For a few years i have had a large capacity battery which extends the life to more than double. The main problem with using an external battery is that it is connected to the phone by a USB lead, and when You pull it out of the pocket you either leave it attached by its lead to the pack in your pocket, or have to drag the phone and a chunk of battery out with the device, not very convenient, also a bit wierd in public.
Having looked on the internet and seen extended batteries that fitted around the phone, I checked the reviews on them online, which did not praise them.
So I decided to make my own.
The armadillo case from mobile fun, was easy to find, it has the advantage of Being in two parts, one wraps around the phone and the other separates with a kick stand, clipping back on when you require it.
Battery selection was next, i wanted a battery that Matched the dimensions of the phone and did not make it too large for a pocket. Capacity and output were big deciders, there were a lot of external batteries that only put out .5 of an amp, which in my experience during heavy use the battery discharges faster than you are pushing in. At least one amp output was on the shopping list.
Eventually I settled on the Pama PNGP2 with a 1 amp power output and 4000mA and had similar enough dimensions to my Nexus 4 (unfortunately I had forgotten something, but more later).
All that remained was to pick up from Ebay a short USB-Micro USB lead to connect it all together.
When the bits arrived I placed the rather nice and solid armadillo phone cover onto the phone and removed the kick stand portion. A small amount of suitable glue stuck the battery to the kick stand before this I discovered that because the battery was the same size as the phone, the camera would be covered up, and so I had to offset the battery to allow for this leaving it overhanging the bottom of the phone. But this did allow the button on the battery to be located on the same side of the phone which protects it from being accidentally pressed.
After leaving the glue to dry I reassembled the parts and plugged the battery in, as expected the phone charged.
A few days later I was able to take the phone out on an amble in the countryside, where before I had been managing the battery to make sure Runkeeper recorded the full 4 hour walk, I could now let the Nexus stay connected and out of Airplane mode and take some photos and still have battery left should I need it. Indeed I have yet over the last few months had the Pama Battery drain more than half way down. As for pulling the phone out of my pocket it has just been a case of grab one slightly larger device and pull rather than taking care over what wires were coming out, and making sure they stayed connected. The case has also been well worth the money protecting the phone from a few potentially disastrous falls. It has also been useful travelling overseas when I haven't been in a position to regularly charge the phone. Mated up with a PortaPow solar charger to charger the battery whilst I keep the phone out of sight.
I have had extended full use out of the phone, more convenient than before, especially now that I often tether my Nexus 7 and Chromebook when out.
Some quick pics.
The battery and the kickstand half of the case, note the power remaining screen and the on/off button.
Battery mounted on phone.
Side view, notice the slight overlap.
Rear view, showing the location of the camera.
Update: MugenPower now sell a Nexus 4 Case/Battery with 4500mAh, very similar but much nicer to my setup.