[Epic 4G Accessories] muyoso:
Just received mine in the mail. Will be uploading pictures and a review here with some battery testing to follow in the next few days.

This is what I bought:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=260697275156

These are selling for as low as 12 dollars shipped on ebay right now. INSANE deal at that price.

Imgur gallery with a bunch more photos:

http://imgur.com/a/sjJB6/1bZGT

First impression:

The battery looks high quality from the outside. The new back that fits the monster battery is a soft touch plastic and fits amazingly well. It feels nice in the hand and actually fits in my holster. Its not as gigantic of an increase in size from stock, around 5mm.

The game gripper accessory works perfectly even with the new back installed.

Measurements:

3500 mAh

weight - 53.61 grams

thickness - 10mm

back cover weight - 13.55 grams

1500 mAh stock

weight - 32.23 grams

thickness - 5mm

back cover weight - 8.45 grams

TESTING:

Fully Charged at 5:42 EST 12/7/10

Phone turned itself off 2:51 EST 12/8/10

Plugged in 2:51 EST 12/8/10

Fully Charged 7:13 EST 12/8/10

Plugged in 12:37 EST 12/9/10

Fully Charged 6:30 EST 12/9/10

Average charging time using wall charger: 5 hours 10 minutes. (Subject to change due to low #'s of samples.)

Alright, I am going to test the Stock battery and compare it to the 3500 mAh by playing 720 Blu-Ray rips from 100% until the phone dies using RockPlayer and measuring the time. Brightness at full, Volume is max, Wifi on. This should be repeatable for various different users with various different batteries to give a benchmark for a batteries potential. The phone is running stock Froyo DK28, with no modifications to CPU speed. DRM services have been stopped.

Why am I testing the battery this way? Because it removes the most variables that I possibly can to convey to you the true potential of the battery. If I tested simply how long it took for the battery to die in my daily use, it brings texting, web use, game use, browsing, screen on time, wifi, 3g and everything else into the mix as variables, and my result will not mean anything to people who use their phone differently. This way, if you get X hours on the stock battery, you can do some simple math and roughly calculate without changing your behavior how long you will get on this battery.

Stock 1500 mAh:

Started 8:24 PM EST 12/8/10

Turned off 1:05 AM EST 12/9/10

Total time: 4 hours 41 minutes

Impressive to say the least.

3500 mAh:

Started 1:10 AM EST 12/9/10

Ended 10:28 AM EST 12/9/10

Total time: 9 hours 18 minutes

What does this all mean . . . .

So on the second total full charge of the battery, I am getting almost fully double the battery life of the stock battery. That is very impressive, especially considering this is only the second full charge the battery has undergone.

http://batteryboss.org/

You can see that OEM batteries typically have between 95-98% real world to rated mAh. So doing some quick math, as I did on page 2, this battery should have between 2829 - 2919 mAh in real world capacity. That places it at 80-83.5% of rated capacity, which is in line with the 3500 mAh Seido battery for the evo. That makes this battery an exceptional value.

Update:

This in no way gaurantees that you will see the same battery life and is a pretty useless figure all around because my usage and signal strength and everything else differs from all of you. But yes, the battery is capable of it. Over a hundred hours of battery life without using juicedefender.