Third Rail Battery Case System For iPhone 4 and 4S

in Outdoors

We’ve all been there; stuck away from home and our iPhone’s threatening to run out of battery. But here’s a solution that we’ve been waiting for, the Third Rail Battery Case System For iPhone 4 and 4S.

The Third Rail System feeds your battery hunger

One of the reasons that some people give for choosing a different phone to an iPhone is that on most other phones you can remove the battery easily, which in the outdoors world is an important feature for a phone, it means that you can carry spare batteries and keep your phone powered during the day which is potentially lifesaving. Let’s face it, the batteries in almost all smart phones, whether it’s an iPhone, Android phone, Windows Mobile 7 or BlackBerry, once you start using its features like GPS and checking your email the battery starts to drain, and fast, with you being lucky to get a full days usage out of the smartphone.

Luckily for iPhone owners there have been several solutions that have become available since its launch to over come the problem of not being able to swap batteries and to keep your iPhone charged. Enter the Third Rail Slim Case and Smart Battery for the iPhone 4 which also works with the iPhone 4S.

Third Rail unpackaged

The Third Rail case offers a currently unique solution for the iPhone 4 owner. It provides a case that can take a removable battery and also using supplied cables power other devices also.

The Third Rail Slim Case and Smart Battery 

This review covers the Third Rail System which consists of the Slim Case, a Smart Battery, a Micro USB adaptor, and a Micro USB to standard USB cable.

Let’s start off looking at the Slim Case. The Slim Case is made from a hard plastic with a soft-touch coating. The case is in two parts that snap together on the iPhone 4 itself. There are the usual gaps on the case to allow access to the various buttons, ports, camera etc. Plus a connector and slots on the back of the case for Smart Batteries to attach.

The Slim Case, when fitted on the iPhone 4 fits snuggly and flush with the front of the iPhone 4.  Without the Slim Case the iPhone is 115mm long, with the case on it is 126mm long. Which means the Slim Case adds 11mm to the length of the phone.

iPhone in Third Rail

Holding the iPhone 4 with the Slim Case on did feel a little weird, and this was due to the increased length of the phone with the case on. The best I can describe it as feeling out of balance in the hand, but with continued long-term usage that feeling disappears.

To charge your iPhone 4 with the Slim Case on you need to use the supplied Micro USB Adaptor and Micro USB to Standard USB Cable, and connect it to the USB port of a PC or Mac, or USB power adaptor, which plugs into the Micro USB port on the Slim Case.

For me to use this as my everyday case I’d need a USB power adaptor, because my normal way of charging my iPhone 4 is to use the dock connector on the DAB radio next to my bed, which brings me to one draw back of the case, if I want to connect the iPhone 4 to an iPad using the camera connection kit to transfer pictures across, I have to remove the case to get access to the connector port of the iPhone because the usual 30 pin dock connector is filled and covered with the case to allow you to charge it.

The Third Rail Smart Battery

The Smart Battery is a 1250 mAh lithium-ion cell that clips straight into the back of the Slim Case piggy back style, the iPhone 4’s internal battery is a 1440 mAh battery so straight away you can see that the Smart Battery will not give you a full charge. If you do the math the Smart Battery capacity is 87% of the iPhone’s internal battery. Due to losses in the power conversion when charging the actual amount of charge you have available to recharge the internal battery according to the manufacturer is between 60-70%. In my testing I saw just below that and was getting around 57-59% therefore the typical usage would be to take your iPhone 4 from say a 30-40% charge up to 100%.

In my testing it was taking approximately 1 hour 30 mins to charge the iPhone 4 from the Slim Battery going from around 20% to around the 80% charge level, charging the smart battery via the USB of my MacBook going from empty to full charge on average took 2 hours 50 mins.

Let’s just step back a little now and describe the Smart Battery. On the battery there is a Micro USB in port used for charging the battery with the supplied cable, a Micro USB port out for charging other devices, a button that when pressed lights up some LEDs that indicate the charge level of the Smart Battery and connectors that transfer the power between Smart Batteries or the Slim Case.


Third Rail battery


One of the key features/benefits of this system is the piggy backing of up to six Smart Batteries to charge the iPhone or other device, when charging something like an iPad using this system this feature is great. It’s also great when doing a multi day hike, you can have up to the limit of six Smart Batteries and only have to use a single charger, it removes the hassle of having to charge a single battery at a time, having to swap them over etc.. This is a great and very time-saving feature.

Listed Weight Measured Weight
Slim Case 25.5g 26g
Smart Battery 39.7g 37.8g
Micro USB adaptor Not given 14.3g
Micro USB to Standard USB Cable Not given 30.3g

One thing that is important to a lot of backpackers is the weight of an item so in the table above I have given the manufacturers stated weights, and those I measured using my digital scales.

Most people will be buying the Third Rail System, which comes with the Slim Case, Smart Battery, Micro USB Adaptor and Micro USB to Standard USB Cable. You get all this for a MSRP of £69.99. The Slim Case can be bought separately and  comes with the Micro USB to Standard USB Cable for a MSRP of £29.99. Smart Batteries can also be bought separately and they come with both cables for a MSRP of £49.99.

This review was written after testing the Smart Battery and Slim Case over a period of a week. Do check back at a later date for the long-term use update, where it will have been used on multi day hiking trips, day walks etc, and tested the areas I wasn’t able to for this review.

The Third Rail System offers a great solution for the iPhone 4 owning outdoors person for powering their iPhone 4 in the outdoors. You can pick up a Third Rail System here.

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