SigFx Energy iPhone Case Contains Smart Battery

SigFX Energy in Lewisville, TX sells a full line of cases for the iPhone 3G/3GS (and iPod touch) that have built-in batteries. I have been testing the X-type design which has a 1,200 mAh (milliamp-hour) smart battery. No power is drawn from the iPhone battery until the external battery is depleted. It's a keeper.

Recently, I decided that I needed an extra battery for my iPhone 3GS, preferably one built into the case, and so I started my trek by purchasing a Mophie Juice Pack Air from a local Apple retail store. However, that customer experience was a disaster, and the product was returned for a full refund.

After reading my blog entry linked above, SigFx Energy offered to send me one of its products for review. I selected the X-type case because it's simple and clean: no cover flap to open. It comes in either white or black to match the iPhone 3G/S colors.

X-type and cable

iPhone 3GS in X-type case

The Battery System

Like the competitors, these battery systems act like an external power source, and you'll see the green battery indicator on the iPhone display when it's in the case -- assuming the external battery has a charge. Power is drawn from the external battery before the iPhone's battery is utilized.

Conversely, when charging, "the case will charge, even if your iPhone was not 100% charged, but gives priority to the iPhone," according to Brett Nelson, the CEO of SigFx Energy.

The USB charger cable, when connected to a Mac, also serves to sync the iPhone to iTunes. The cable worked the first time, every time on both units I tested. (More on that below.) It charged and synced even when plugged into the back of my 24-inch Apple LED Cinema Display, but that was only at first.  Over a longer period, one should use a direct USB port on the Mac to support the current required.


  • 1,200 mAh battery (same as iPhone)
  • Output current: 500 mA
  • Output Voltage: 5 V
  • Charge time: 3.5 hours
  • Case weight: 68 grams (2.4 oz.)
  • Life cycle: 500 charges
  • WWi Certification from Apple
  • Warranty: 1 year

A red LED on the case edge glows red when charging and goes out when fully charged. A set of four blue LEDs on the back reveals the state of the battery, just as with the old PowerBook batteries.


The X-type does not come with a protective film for the display as some cases for the iPhone do. However, I already had one installed, and the SigFx case does not interfere. I recommend protective screen films from, available from Apple.

Unlike the Mophie Juice Pack Air and, I believe, the Phonesuit MiLi Power Pack, which wraps partly around the edge of the iPhone just a bit, the SigFX X-type leaves the silvery edge of the iPhone exposed. (Note, however, that Phonesuit appears reluctant to have its products reviewed, so I can't say for sure.) Also, it was my choice to select that kind of case, and there are other cases in the SigFx line that afford complete protection, for example, the XR model. That model also has a larger battery, 2,000 mAh. I mention this not as a negative, but rather a detail of the various cases designs to be aware of. These other cases with a cover flap also eliminate, mostly, the need for a protective film and fully protect the iPhone, including the edges.

X-type edge view

X-type edge view

The X-type case is soft and easy to grip without collecting lint like the Incipio case I used before. The material used on the Incipio is ultra soft, and I had to use Scotch Tape frequently to remove dust and debris. The SigFX Energy X-type case always looks good.

Day to Day Use

I lived with the X-type case for over a week, took it with me on the weekend, shopping, eating out, etc. Having that battery indicator on the iPhone always showing 100 percent is a nice feeling compared to how I was living before. This kind of case is also nice if you're like me and keep forgetting to turn Wi-Fi on and off as needed when out of the house.


X-type -back 

Back of case showing status LEDs (Soft cloth is the reviewer's)

Documentation & Warranty

There is a small booklet included, a little smaller than the iPhone, that has 18 pages and includes charging procedure, features, recycling, warranty and contact/customer service info. While the documentation strongly suggests that one fully charge the battery before inserting an iPhone into the case, it really isn't necessary. The advice is just there to make sure the customer has a good experience.

The first unit I received had a very slight curing issue with the paint, and in some places on the back less than 5 mm long, there was some almost unnoticeable flaking. I had to use my lighted magnifying glass to be certain. SigFX, when advised, did several things. 1) They sent me a replacement. 2) They checked inventory and found no other cases with that flaw. 3) Briefed their QA people to watch for other such flaws, and 4) Affirmed that any customer who might get such an X-type case with that minor flaw would receive a replacement at no cost. I was not greatly concerned after that.

Closing the Case

Some companies, when they're having problems, clam up. That's really frustrating to the paying customer. However, with SigFx, there was a very, very open line of communication. I am confident that any other customer will get the same kind of attention and customer service. When companies have strong products and stand behind them, they're will to communicate and do what it takes to make the customer happy. Based on my bad experiences with Phonesuit and Mophie so far, I would recommend a serious look at the products offered by SigFx Energy.

Product: X-type

Company: SigFx Energy

List Price: US$69.95



Protective case with good grip, built-in battery with same capacity as iPhone, smart charging and discharge, LED indicators for charging and battery status, all iPhone ports & sensors preserved, Apple certified, available in colors to match iPhone, USB cable is long enough.


No protective film included for iPhone display. This model leaves iPhone edges exposed. (Others do not.)