Third Rail Slim Case and Smart Battery System for iPhone 4 Review

We use affiliate links. If you buy something through the links on this page, we may earn a commission at no cost to you. Learn more.

third rail slim case 1You choose a sleek new smartphone, then the internal war begins:  case or no case? Cases can obscure the looks that attracted you to the phone in the first place or make it much heavier.  Or you find out that all those features drain your battery so quickly that you can’t make it through a long day without needing to recharge.  External batteries can keep you going all day, but it’s hard to use a phone with a big battery pack dangling from the charging port.  Some cases have built-in batteries, but they are too big and heavy to keep on your phone all the time.  Third Rail offers a case and external battery system that gives you what you want – protection and power – without the things you don’t want – bulk.  Let’s look at the Third Rail System for iPhone 4 I received for review.

In the Box
third rail slim case 4Slim Case
Smart Battery
USB to micro USB cable
USB adapter for charging other devices

Note: Some images may be clicked for an enlarged view.

third rail slim case 2third rail slim case 3The Third Rail Slim Case is a thin, two-piece case that slides on to your AT&T or Verizon iPhone 4. The case is made of hard plastic and is only available in black.  The outside has a rubbery coating; inside is smooth and shiny.  The case is a snug fit. There are three little copper rails on the back of the case that act as the battery contact.

third rail slim case 6
Bottom with power switch and sync/charge connector.

third rail slim case 7third rail slim case 8third rail slim case 9The Slim Case covers the back and sides of the iPhone, but it leaves the back camera, power button, headphone jack, microphone, volume buttons, and the mute button open.  The bottom of the case extends past the bottom of the phone, and there’s a standard Apple docking connector inside that plugs into the iPhone 4.  Openings are left on both sides of the bottom so you can still hear the speakers.  There is also a micro USB connector and a switch on the bottom of the case.

The Smart Battery is a thin black rectangle with three of the copper rails on the outside and a rechargeable 1250mAh lithium-ion battery inside.  The back of the battery has four tabs that attach it to the case and three copper contacts that will line up with the rails on the case.

The battery is about 3.2” long X 1.75” wide.  The case is about 4.8” long X 2.4” wide X 0.4” thick without the battery or 0.6” thick with the battery.  It weighs about 0.9 oz alone, or 2.29 oz with the battery in place.

You’ll notice I gave measurements with and without the battery.  The beauty of the Third Rail System is that you leave the thin, protective case on the iPhone 4 all the time, but you only attach the heavy battery when you need to supply extra power to your phone.   Simply snap the Smart Battery to the back of the Slim Case and flip the switch on the bottom of the case to start recharging your iPhone 4.

You won’t have to take the Slim Case off to charge and sync the iPhone 4.  Connect the phone to your computer with the included micro USB cable to sync and charge it.  If you install the Smart Battery, both the phone and battery will be charged.   Circuitry directs current to charge the iPhone 4 completely before sending power to the Smart Battery.

The 5 LEDs on the bottom of the battery blink as it charges.  Charging is complete when the lights turn off.  There’s a button under the LEDs.  Press it and the LEDs light up to show the remaining charge.

Because the battery and case are separate, you can buy extra Smart Batteries to be sure you’ll never run out of power.  You can charge the battery alone by plugging the micro USB charging cable directly into it.  The batteries have the connectors on the back and the copper rails on the front, and they have tabs on the back and slots on the front.  You can connect all your batteries together and charge them all at once.  Even better, you can connect all your partially charged Smart Batteries together and they’ll consolidate all their power to top off power on the fullest battery.

Finally, you’ll notice an extra connector on the bottom of the Smart Battery that’s marked out.  If you use the short USB adapter cable, you can use the Smart Battery to charge up another device, such as a Bluetooth headset, MP3 player, or similar items.  You can also charge your iPhone 4, Smart Battery, and another device all at once using the micro USB cable.  Now you know why they’re called Smart Batteries!

third rail slim case 5third rail slim case 10I found the case to be fairly comfortable on my iPhone 4.  It added weight, but it didn’t seem to change the size of the phone otherwise.  The case didn’t interfere with the operation of the back camera at all.  Since it leaves the front of the iPhone 4 completely open, there is no chance it will interfere with the front-facing camera or the ambient light or proximity sensors.

It felt much heavier with the battery in place, but it wasn’t uncomfortable to use – especially when you remember this is only a temporary configuration.  My iPhone 4 had about a 71% charge when I plugged in the battery.  It was completely charged (the lightning bolt had changed to the plug on the battery icon) in 67 minutes.  The Smart Battery still showed 4 out of 5 LEDs when I checked its power.  The 1250mAh capacity of the battery is only about 87% of the iPhone 4’s 1440mAh battery.  Inefficiencies of transferring power inherent with any external battery will result in about a 60-70% charge of a completely drained iPhone 4’s internal battery from the Smart Battery.

I disconnected the Smart Battery from the iPhone and used it as an external battery to charge up my iPod nano.  The nano showed about 50% power to start.  It was charged to 100 % (power plug showing on the battery icon) in about 71 minutes.  The Smart Battery was still showing 4 out of 5 LEDs.

The Third Rail System is very flexible.  Right now, they only offer the Slim Case for the iPhone 4, but they mentioned plans to introduce cases for other devices in the future.  That means you’ll be able to use the Smart Batteries you own with a new phone just by purchasing a new case.  It also means that everyone in the family can have Slim Cases for their phones and share a Smart Battery.  You can purchase the complete System for iPhone 4 (Slim Case, Smart Battery, and cables) for $89.99.  Extra Slim Cases (available for iPhone 4 only right now) are $39.99, and an extra Smart Battery with cables is $59.99.

I usually don’t like phone cases with external batteries built in because they are clunky and heavy.  I do like the Third Rail System for iPhone 4.  Most of the time, my phone is in only the Slim Case, which adds little bulk.  I only have to use the heavy battery when I need it.  Unlike most other battery cases, the battery is always available for emergency power for other devices, too.  And it’s flexibility means that it won’t be obsolete the minute you upgrade to the iPhone 5.  The only thing I don’t like is that it’s only available in black.  I’m bored with nothing-but-black electronics.


Product Information

Price:System is $89.99; extra Slim Case is $39.99; extra Smart Battery is $59.99
Manufacturer:Third Rail
Retailer:Third Rail
  • iPhone 4
  • Battery only installed when you need it
  • Case is slim and light
  • Battery can be used as an external power source for other devices
  • None, but I do wish it came in other colors.

2 thoughts on “Third Rail Slim Case and Smart Battery System for iPhone 4 Review”

  1. Gadgeteer Comment Policy - Please read before commenting
  2. Meagan basilone

    I dont get it why people like this thing. It’s such a novelty product. So now Im suppose to carry an iPhone, a specialty iPhone case and separate battery. This thing might be cool the first week yo use it, like any novelty. But after a few weeks youlll realize, that its a pain in the ass. You’ll easily misplace the extra battery. What am i suppose to carry an extra battery in my pocket at all times now? Because the thing is ugly and fat with the battery on. I mean look at the picture. You’ve completely killed the sexyness of the iPhone. Its also expensive and it cant give you a full charge. I’m all about the Phonesuit Elite now. Superior design for sure.

  3. Mark Rosengarten

    I have the Mophie Juicepack Plus and I love it. Sure it makes the phone thicker and heavier, but I have extra power with me at all times. A LOT of power that recharges my phone very quickly.

Leave a Comment

Your email address will not be published. Required fields are marked *