[EVO 4G Accessories] mitchellvii:
The great question:

Is it better to 1) carry extra batteries with me and just trade them out as they die but maintain the light, sleek form factor of my EVO, 2) get an extended battery that will make my phone thicker and significantly heavier (resulting in fewer case choices or cradle fit issues) or 3) get an external travel battery that plugs into my phone via USB and recharges my battery with another battery?

Well each has it's pluses and minuses:

1) Extra Batteries: The problem is, of course, transporting them. You also need to buy an external charging dock to keep them juiced and the phone has to be taken apart to replace them. With some cases such as the Otter Defender, this can be a significant hassle. As far as transporting them, it is easy to buy an unobtrusive $10 leather zippered pouch and carry them that way.

2) Extended Batteries: Easily charged in your phone and not requiring replacement during a long day, these batteries are an attractive option. However, say goodbye to your sleek and slim EVO. These add significant heft to your device and make it twice as thick. Also, unless you pay top dollar for a name brand, you risk having a "fake" product of questionable build and even more questionable capacity. Watch a video of a "Lion" battery fire and you will realize you don't want to play with cheap knockoffs any more than you would buy knockoff medicine from a guy in China to save a few bucks. And oh yeah, good luck finding a case that fits your "pregnant" evo.

3) Portable Battery Chargers: Again, these can be an attractive solution. They can come in many sizes (up to 8000 mah) and can recharge your phone even as you use it. The issue is bulk. One 5400 mah device is about the size of your EVO. So, imagine carrying 2 EVO's with you (never mind the USB cord). Compare this to carrying a spare 1500 mah battery in a small leather pouch (which you would hardly notice is even there). Also, these charge your phone using USB cable. This means a maximum charging rate of 500 ma. If you are using your phone for power intensive tasks such as Google Navigation, your phone will still run out of power even if it is plugged in.

CONCLUSION:

Weighing all of the factors, I recommend getting a couple extra 1500 to 1750 mah OEM batteries along with a wall charger (don't be cheap - these things can go boom). Simply carry them in a small zippered leather pouch you can pick up anywhere they sell wallets. A fully charged battery in your phone and just one of these "stand-bys" should get you through even the most grueling day.

The only hassle here is physically switching them out; however, that is less of a hassle than dealing with a "double-thick EVO" extended battery or an "extra EVO in your pocket" external travel battery. You should only have to change the battery out once in a 24 hour period. With the other solutions, you have to deal with their negative aspects 24/7.

You keep your slim form factor, you not are limited by case choices and you extend your power - win.

** This conclusion assumes the user will eventually have access to AC power to recharge sometime in a 24 hour period. For camping, etc, where you will be away from wall/car juice for extended period, the external travel battery may be your best choice (and you can carry it in your backpack).