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Here's a well thought out and very flexible way to have extra emergency power for your portable devices.

The Third Rail External Battery System can work with a wide range of different electronic items.

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Third Rail External Battery System

A great way to add extra battery life to your iPhone and other devices

Third Rail Battery System

The Third Rail Battery System comprises a case for an iPhone 4/4S and separate batteries that can be mounted on the case or used by themselves.



Battery technology is failing to keep up with the new power demands made of it by each successive new model of cell phone, and so smart phones struggle to offer good battery life.

This is particularly a problem with Apple's iPhones, because you can't swap batteries over in the middle of the day.  The only way to add to your phone's power charge is with some sort of external battery.

Here is one of the most elegant approaches to solving this need, which works not only for the iPhone 4 and 4S, but also for many/most of your other portable electronic devices too.

Third Rail Battery System - What You Get

The Third Rail Battery System comes attractively packaged in an easily opened box.

Inside is a case into which you fit your iPhone 4 or iPhone 4S, a separate battery, two different connector cables, and a helpful well written short manual.

There is no charger supplied with the unit.  But that is more a blessing than a disadvantage, because the unit can be charged from any standard USB type charger, and you probably have more of those than you can count, already.  It is great not to have another device which requires its own dedicated charger due to having nonstandard connectors.

The unit comes with a 30 day money back guarantee, and a one year warranty.  Both are generous and better than industry averages.

The complete 'system' - ie a case for an iPhone 4/4S and a battery, retails for $89.99.  You can also buy cases by themselves for $39.99 and batteries for $59.99.  Indeed, if you should lose the connector cables, you can buy them too ($9.99 each).

The products are available through Third Rail's website.  They can also be purchased through (and Amazon will probably save you the shipping costs).

Third Rail Battery System - What It Does

1.  In its simplest form, this is a wonderful way of carrying additional recharge power for an iPhone.

2.  But - and it is a good but - the Third Rail system does a lot more than just recharge a dying/dead iPhone battery.  It has an external power socket that can be used to then charge any other typical mobile device (ie anything that uses a 3.7V LiIon type battery for power, and which can be charged from a USB socket).

It won't charge high power devices such as laptops or large tablets (eg iPads) but anything that uses the standard USB and 500 mA of charging current can be powered from a Third Rail Battery.

3.  Unlike most other external power case solutions for iPhones, the Third Rail system uses a detachable battery.  So you can have two batteries for the one case, giving you even more emergency power (and saving you hassle, space, weight and money compared to having to carry two complete cases.

4.  Not only can you have two batteries and one case/phone, you could also have two phones, two cases, and one battery.

5.  If your entire office (or household) uses iPhones, you could have multiple cases and multiple batteries, and simply rely on the intelligent charging of the Third Rail batteries to ensure that whenever you needed a charged battery, there was always one available.

6.  Multiple batteries can be stacked together.  They intelligently 'talk' to each other and manage their power so as to consolidate the most power in the fewest number of batteries - so rather than having maybe five or six half charged batteries, they concentrate all their power into two or three fully charged batteries.

They also intelligently charge themselves so that the most full batteries get topped up first, meaning you get fully charged batteries, one at a time, sooner than if they were all charged concurrently.

In total, this is a tremendously flexible system that can be mixed and matched to give you exactly what you want, without requiring you to over-buy things you don't want.  Not only is it flexible, but it is also very simple, with the intelligence being built into the Third Rail system rather than being required of you, its owner/beneficiary.

About the Third Rail System

There are two components to the Third Rail System - the case and the battery.  Yes, there are connecting cables too, but they are of lesser importance.

The Case

The first step is probably to put your iPhone 4 or 4S into the protective case.  This is a very slim case that fits around the back and four sides of the iPhone, leaving the front open.  An iPhone 4/4S measures about 2.3" x 4.5" and is 0.4" thick.  Adding the Third Rail case increases its external dimensions to about 2.45" x 4.9" and its thickness up to 0.46" - not very much more.

As for weight, the case adds less than an ounce (0.85 oz to be precise) to the weight of the phone (which is 4.9 oz to start with).

These dimensions are similar to most other iPhone cases (although iPhone 'bumpers' are a little smaller/lighter).

The case has an Apple connector which slides into the connector on the phone, and duplicates the connector outside the case, but in the form of a standard micro-USB connector rather than a proprietary iPhone connector.  But - fear not.  You can still connect your iPhone to a charger or to iTunes via your computer through a regular micro-USB cable and the micro-USB connector on the bottom of the case; you never need to take the phone out of its case to use with a dedicated iPhone cable.

That too is a benefit - it reduces the number of different types of connecting cables you need to travel with and keep close to you.

Also on the bottom of the case is a slide switch.  Slide it one way and you see an orange dot, which indicates that the Third Rail system is 'off' (just like the orange dot on the iPhone's mute switch indicates when the volume is off).  Slide it the other way and that means the Third Rail system is active and ready to transfer power into the phone.

On the back of the case is a connector onto which the external battery can be clipped.

The Battery

The Third Rail battery is a separate small device.  It measures 3.3" x 1.8" and is about 0.3" thick, and weighs a mere 1.4 oz.  You could fill your pocket with half a dozen or more of them if you chose to do so, but there is little reason to carry more than one or perhaps at the most two.

On one side are four connectors to clip the battery to other batteries or to a case, plus a 'male' power connector.  On the other side are four slots to receive connectors from other batteries being stacked on top, and a female power connector.

On the bottom are two sockets - one to receive charging power in from an external charger, the other to give charging current out to other external devices.

There is also a five element LED on the bottom and a 'press to test' button; when you press the button, the LED reports on the level of charge in the battery.

The battery stores about 1250 mAh of power, slightly less than an iPhone's internal battery (which is about 1400 mAh).  But see below for a surprising discussion about how you actually get more life out of 1250 mAh than you do out of 1400 mAh.

Using the Third Rail System

Using the Third Rail System is easy.  If your phone needs a top up charge, put a battery on the case and turn on the charge button.

When the topping up is complete, turn off the charge button (or simply remove the battery from the case back).

You can leave the battery connected to the case all the time.  I've tried it both ways - with battery left on and with battery off.  If you want to keep your phone as slim as possible (eg in a dress shirt pocket) you'll probably want to keep the battery off the phone when you're not using it.  But if space isn't quite so critical, you may as well leave it on, making the battery harder to lose.

If you have an external charger, simply connect it to the connector either on the battery or on the case.  Either which way, it will first charge the phone's internal battery, and then secondly charge the external battery (or multiple batteries if they are stacked together).

Third Rail recommend you connect an external charger to the socket on the case, because if you do this, it will charge at a slightly faster rate.  But apart from shaving a few minutes from the total charging time, there is no real other difference.

If you have another mobile device that also needs topping up, simply connect its charging cable to the USB output adapter cable that came with the Third Rail system.  It doesn't matter if the battery is on a phone case or not, either which way, it will start to charge the new device.

Multiple Battery Bricks

One of the very clever features of the Third Rail design is that the batteries can be stacked on top of each other, creating a larger capacity multi-cell battery.

These stacks of batteries can be created almost without limit, stacked as high as you wish, but Third Rail recommend between six and ten batteries per stack is probably enough for most purposes.

When batteries are stacked, they concentrate their power in the fewest number of fully charged batteries, so that even if you don't have a charger with you, you can pool the power in several partially charged batteries to get some fully charged batteries, avoiding the need to carry multiple partially charged batteries with you.

How 1250 mAh Lasts Longer than 1400 mAh

Although these external batteries have slightly less capacity than the internal iPhone battery, the surprising reality is you can get more benefit and usage from them than you can from the internal battery.

This needs to be explained.  So, here goes :

With the iPhone's battery, the chances are that whenever you go somewhere with the phone, the battery is not at 100% to start with.  Maybe it is at 90%, or some other partially full charge.  So you start off with less than the full capacity of the battery.

And when the battery starts to drop down to 20% or less, you start to get really panicky and stop using the phone freely, limiting its use only for emergencies.

So the actual 'comfort zone' of usage is maybe only 70% of the full battery charge, in other words, 70% of 1400 mAh, which is just under 1000 mAh.

But with the external battery, you can fully charge it up to 100% of power, and then when you choose to use it, you can fully transfer the entire 100% of its charge into the iPhone.  Apart from some efficiency and transfer losses, you are otherwise getting the full 100% of the 1250 mAh as practical, 'comfort zone' usage.

Multiple Systems

Because the Third Rail Systems can either be bought as complete systems or as separate components, it is possible to come up with different mixes of batteries and cases to reflect the situation you are in.

For example, in an office with a dozen sales reps, maybe they only need to have six or eight batteries - the reps only grab a battery when leaving the office to go out on sales calls.

On the other hand, if you are a single user, maybe you want to have one case but two batteries, so you always have a fully charged one plus a spare to be in use.

Any other combination of cases and batteries can also be used for whatever circumstances apply.  And, if you should lose a battery (or case for that matter, too) you can simply buy just the battery or case as needed rather than needing to buy a complete new system.


The Third Rail System is a brilliant example of a very well thought through product that has a great deal of flexibility and bonus functionality, way in excess of that normally found in a simple, single application, external/emergency battery for an iPhone.

It is easy to understand and use, compact, light weight, very useful, and fairly priced.

A complete system is $90, available either direct from the manufacturer or from .  You'll probably get it quicker from Amazon, and probably get free shipping too.

Definitely recommended.

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Originally published 4 Nov 2011, last update 21 Jul 2020

You may freely reproduce or distribute this article for noncommercial purposes as long as you give credit to me as original writer.

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