iPhone Battery Case Review: Third Rail System For iPhone 4 & 4S

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We’ve discussed it before — battery life is the Achilles heel of mobile electronics. Devices are faster and more powerful than ever, and battery technology just can’t keep pace. Now word comes that, despite claims to the contrary, the iPhone 4S may not have battery life that is on par with the iPhone 4. So what are those of us who depend on our smartphones for just about everything supposed to do? There are some great tips and tricks for saving battery life, but most require temporarily crippling some of the phone’s features. But who wants to constantly be tweaking one setting or another in order to squeeze some extra life from their phone? What other option is there? Get extra batteries, that’s what!

Sure you can carry an external battery or two with you. We’ve reviewed some great ones, but that’s a lot of extra bulk to carry around. You can also opt for one of the many battery cases that are now available. There are some awesome ones, but all of them add weight and bulk to the phone. Travis took a look at the Third Rail system earlier this year, but now this solution is more timely than ever!

The Third Rail’s Slip Case for iPhone 4 and 4S is a super thin case to which you can connect a battery when needed. When you don’t need the extra juice, however, you can simply remove and stow the battery. There are even more tricks offered by this unusual case, so let’s take a closer look…

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From Third Rail:

The Third Rail™ System includes the Slim Case for iPhone 4 with a slide-on Smart Battery. Understanding that your daily power needs may vary, The System allows you to add power when you need it and remove it when you don’t! The Slim Case is a sleek, everyday protective case with a high quality, soft-touch feel. The Smart Battery can also function as a standalone backup battery to power other devices via USB Adapter.


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Ultimate Flexibility: Daily power usage may vary – we feel that your solution should vary with it. The Third Rail System gives you the power to choose when/where/how to add additional power to your everyday protective Slim Case.

Hot Swap on the Go: For every day usage, we recommend that you attach one battery to the Slim Case at a time. No need to stack multiple on your case- simply swap out for fully charged ones on the go. However, for convenient charging from a single power source, you may stack your Smart Batteries on your Slim Case and charge everything from the micro USB on your case.

Share your Power: The Third Rail™ Slim Case is compatible with all Third Rail™ Smart Batteries so you can easily share Smart Batteries among family, friends, and coworkers.

Complete Coverage: Durable hard-shell protection with a soft touch coating provides access to all iPhone 4 features.

Power Wherever You Are: Keep Smart Batteries in your pocket, bag, or car for convenient power anytime.

Power When You Want It: The integrated on/off switch on the Slim Case allows you to choose when you want power to flow from your Smart Battery to your iPhone. Simply flip the switch on the bottom left of your Slim Case to change it between stand-by mode (red) and charging mode (black).

Universal Power Solution: Using your Smart Battery, charge your mobile phone, Bluetooth headset, MP3 player, gaming device, etc. using micro USB Adapter (included).

Future Proof: Smart Batteries are compatible with existing and future Third Rail™ cases, eliminating the need to purchase new charging accessories or battery cases with each new mobile phone purchase.

Apple Certified: Officially a “Made for iPhone 4” product.

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As you can see, this is a slider-style case. You slip the iPhone into it bottom first and then put the cap on top. It is a tight fit but not overly so. That means you won’t feel like you have to jam the phone into the case the way you do with some other slider cases.

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The case adds minimal weight and bulk to the phone, and it has clean lines when you look at it from the side. That’s actually the idea behind this modular design. Add on the battery when you need it. Remove it when you don’t.

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The front view also reflects the tight, minimalist approach the case takes. Sure, the case adds a bit to the iPhone length/height but that is always going to be the case since there needs to be a connection to the 30-pin dock connector on the bottom. And, after all, it doesn’t add THAT much height and the cutouts for sound to pass through are quite subtle.

Yes, from the sides and front the case is as clean as any slider case we have seen.

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From the back, however, the case tells a different story. In order to attach the battery pack to it there needs to be a connection system. That takes the form of the four small cutouts on the back. (You can see the upper two in this shot.) There also needs to be a way for the battery to send power to the phone. That arrives in the form of the three contacts you see toward the right. While this works perfectly, aesthetically it leaves something to be desired.

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The battery pack clips right into the case and, once there, is held securely. This design reminds me a lot of the first generation of conductive-charging iPhone cases. Each of those had a thick plate on the back that made contact with the charging station. In this case it is the battery that “bumps out” from the case but the result is the same — what was once a thin, comfortable case now has added weight and bulk that makes it a bit less comfortable to hold.

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In this picture you get an even better sense of the added bulk the battery adds. It isn’t “bad”, but it is quite noticeable and does detract from the clean lines.

You can also see two microUSB ports and the five charge indicator lights between them. One port is used to charge the 1250 mAh battery. The second is there so you can use the battery to charge other devices. Yes, unlike other battery cases Third Rail’s offering charges the iPhone AND non-iPhone devices.

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Another piggy-back shot and you get an even better sense of the design. On the right side of the case in this shot you can see the on/off toggle for the battery. As Judie taught me last year at CES, the best way to use an external battery is NOT to let the phone run down and then switch on the battery but rather to top off throughout the day. It works beautifully.

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Speaking of the battery capacity, I was underwhelmed to learn that the battery used by the system offers just 1250 mAh. I’ve become used to using external batteries that have double or triple that and, at least for me, 1250mAh doesn’t seem like enough. Third Rail thought of that however and there is a cool trick up the cases’ sleeve. You may have noticed that there are gold contacts on BOTH SIDES of the battery. The reason for this is quite simple — you can purchase additional batteries and piggyback them one on top of the next. It does get pricey, but this means 1250 mAh can be turned into 2500mAh and more. That’s pretty neat.



Slim Case: 4.96 in x 2.43 in x 0.46 in; 0.85 oz

Smart Battery: 3.29 in x 1.83 in x 0.27 in; 1.4 oz

Battery Capacity: 1250 mAh lithium-ion polymer battery

Package Contents: Slim Case for iPhone 4, Smart Battery, Micro-USB Cable, USB Adapter, User’s Manual

Case Compatibility: Works with every iPhone 4, iPhone not included

The Third Rail System For iPhone 4 and 4S is a unique design that does exactly what it promises. It lets you have both a slim, light protective case on your phone AND a battery case that will give you the extra juice you need to make it through the day when you don’t have access to a wall charger. Despite the battery aspects breaking the clean lines of the case, without the battery attached it feels great in the hand. With the battery attached the case it bulkier but still thinner than many other battery cases. The fact that you can piggyback batteries is more than a bit neat.

Yes, the Third Rail System For iPhone 4 and 4S delivers exactly what it promises. And while I don’t love the fact that the battery is just 1250mAh I do think it would be satisfactory for most people. Then again, since the battery will likely sit in your bag or purse much of the time I am left wondering what real advantage this has over a completely separate external battery that gets pulled out when you need it.

You can get more information on the Third Rail System For iPhone 4 and 4S on the company website.

MSRP: System (case and one battery) $89.99; Case alone: $39.99; Smart Battery: $59.99

What I Like: Thin, light case when you want it, extra power when you need it; Batteries can be piggybacked; Charges more devices than just the iPhone; Battery can be used completely separately for other devices

What Needs Improvement: Just 1250mAh; gets pricey quickly if you buy more batteries; With the battery attached it has a rather odd feeling to it

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About the Author

Dan Cohen
Having a father who was heavily involved in early laser and fiber-optical research, Dan grew up surrounded by technology and gadgets. Dan’s father brought home one of the very first video games when he was young and Dan remembers seeing a “pre-release” touchtone phone. (When he asked his father what the “#” and “*” buttons were his dad said, “Some day, far in the future, we’ll have some use for them.”) Technology seemed to be in Dan’s blood but at some point he took a different path and ended up in the clergy. His passion for technology and gadgets never left him. Dan is married to Raina Goldberg who is also an avid user of Apple products. They live in New Jersey with their golden doodle Nava.