It is pretty simple to test iphone battery life by measuring movie playing time. Here is the procedure...
1. Method 1- Fully Charge iphone through AC charger. It will take 2-3 hours to fully power up an iphone. After fully charge it up, load 11 long movies onto iphone using iTune software, play 11 movies with non-stop mode. Count the hours. The battery life for playing movie is about 5-6 hours without connection with an iPhone backup battery. After that, fully charge the iphone up again, this time, connects iphone with an IMP500 iphone backup battery through an iPhone connector, play the long hours movie and count the hours again. This time the measuring time will be surprisingly longer, which will be 38 hours (About 10+ movies) See the measuring table below. This IMP500 is a a perfect unique iphone accessories
2. Method 2- Fully drain out the battery for iphone, let the iphone battery completely drained out. Fully charge up IMP500 iphone backup battery using AC charge. Use IMP500 to power up the iphone. If we test the battery life this way, we found iPhone movie playing time drop to 15 hours only if connects with IMP500 iphone backup battery. It takes more power to power up iPhone if the battery is completely drained out. But this model is still very very powerful if compares with original iPhone battery, which is only 1250mAh. IMP500 holds 5000mAh battery capacity