I used my corporate discount to get the Motorola Portable Powerpack P893 from Verizon. It is 1800 mAh. I am happy with it and it fits my needs. The nicest thing about it is that it is pretty small and thin. Given it is not nearly as small as an extra battery, which i was used to carrying around when I had the DX, but it will fit comfortably in your pocket and you can easily still hold the phone in your hand with the battery pack right behind it. It is about as thick as the Razr is at the top where the camera is and is about the size of the area where the Kevlar is, but a little bit more narrow. When fully charged it will give you an extra 60-70% charge. It takes a while (30 min? maybe, I never really timed it) to fully discharge the battery pack, so it gives you a little extra time of charge. I can't say anything about how well the other battery packs that you can find on Amazon or ebay work, but if you get one that is 5000 or 8000 mAh it will be much larger than this battery pack. So they would provide a lot more extra charge, but would not fit in your pocket and would be really awkward to hold onto if you need to use the phone while it is charging. So it really comes down to what you plan on using the battery pack for. Do you need to have more than extra 60% charge or do you want something portable that you can easily carry around in your pocket with your phone. The only times I have needed to use my battery pack was when I was outside or somewhere I am not near an outlet for an extended period of time, so I need to be able to carry the battery pack in my pocket with my phone.
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