I use my EVO 3D a lot… I mean a whole lot. I use it as part of my work (I'm on call 24×7), for play, and for one of the lesser known functions it has: as a phone. I have spare wall chargers, car chargers, and even keep a couple of spare batteries ready.
There are photos out there of me in a bar with a car jumper battery plugged into my phone. No kidding. I've been part of the huddled masses at an airport vulturing for a wall outlet after watching movies on a plane for four hours on my phone.
Seidio recently released a product called the Charging Vault ($59.95) and provided me one to play with. It's a wall charger that can continue to charge your phone after it's unplugged from the wall. It sports a 2200mAh battery built into it and two USB sockets that you can either plug your charging cable into, or the retractable charging cable that comes with it.
The cool thing about this is that it's portable; the electric prongs fold up and you can slip it in your pocket if you need to take it with you. The retractable cable folds back up to about two inches – perhaps it's a bit less of a footprint than a regular cable but not by much. Since it's USB you can feed your other friend's phones as long as they brought charger cables too.
Although Seidio's site only mentions that you can charge two devices at once while plugged in, I was charging my EVO 3D and 4G at the same time this morning without seeing either phone showing negative drain. So perhaps it can charge two at once, or maybe it charges them extremely slowly.
The Charging Vault doesn't weigh much, coming in at a reported 6.1 ounces (that may be the entire package though), so carrying it around on a hiking or camping expedition will not wear you out as it only weighs about as much as three batteries.
The 2200mAh capacity means that if you have a stock HTC EVO 4G you can completely charge your EVO (from dead) once, and then charge it a little over half full. Or you can give two dead EVOs a 75% charge. If you're on an EVO 3D you're looking at one full charge from empty, and then about a third of a charge. If you just need to make it through a long day, it'll handle it fine.
On the face of the charger are four recessed battery indicator lights to give you a feeling of where you're at on power remaining on the battery. There's also a power button as the thing shuts off when unplugged and not in use, or your phone reaches maximum charge. It's always on when plugged in though.
The Seidio retractable charger cable is neat, but I don't like it too much. It's amazingly portable and won't tangle when chucked into a purse, but I think if I sat on it, I would crush the thing so badly it wouldn't even be recognizable. So for packing/purses/luggage, good; jean pockets, bad. Since I'm using it the jeans/pocket way, I say boo. I also don't think it saves any space – thinner cable, but retractor mechanism takes more space. It's good for keeping the tangle down though.
The only thing I really wish this came with is a hide-away pocket for the cable, or perhaps a universal fitting kit for when you meet someone who needs a charge but doesn't use the USB connectors that we use on our EVOs. As I mentioned earlier, though, as long as they're packing their own USB cables they can plug in.
This thing saves me a lot of space since I don't have to carry around extra batteries and chargers.