We seldom feature iPhone cases around here but this new one from Third Rail has an interesting proposal. Instead of a built-in battery ticked into a bulky case, Third Rail made it optional as a slide-on pack.

The case is made of solid polycarbonate materials in a matte black finish. The inside, at the bottom end there’s the proprietary 30-pin Apple USB port while the top section slides out to make way for the iPhone to fit inside the case.

The case itself is relatively thin (around 2mm) but the construction extends the height of the whole assembly by at least 2 centimeters at the top and bottom end.

The back panel has 4 small, rectangular holes where you can snap in the external battery. There’s a set of 3 metallic contact points around the middle section for the charge to pass thru.
At the bottom of the case is where the micro-USB port is located along with a switch for the charger.

The slide-on battery is also interesting. It comes with 2 micro-USB ports — one for input and one for output (probably to be able to daisy-chain the power charging).
The back of the battery also has the same 3-pin contact points which allows for another slide-on battery to ride on top of it. It’s a pretty interesting proposition but I reckon the iPhone might not be that usable when you have several batteries stack on top of each other.

The Li-Ion battery is rated at 1250mAh and is able to re-charge my iPhone 4S from 9% to 70% before it completely drains up. With the case snapped on, you can now hook up your iPhone via a micro-USB charger as well.
The case is available in local stores like Digital Walker or Digital Hub for about Php3,850. Seems to be a little on the expensive side though (that is, if you consider buying a separate slim case and external battery instead).
Anyway, if you have an iPhone 4 or 4S, you might want to have this review unit for yourself.
So we’re raffling it off with Rafflecopter below.
Update: And our winner is…

Congrats! Email me for instructions on how to claim your prize.
Disclosure: Digits Trading provided for the review unit. They are also a display banner advertiser on this site.

I own an unlocked iPhone 4S! Got it last January.
We all know about its poor battery life. Now, this will do the trick! :P