They are probably having you fully test it for them before sending it back for any reason. If it is Lithium Ion there is no denying the physics involved.
this came off the mugen site, and my instructions that came with my hyperion says the same, please contact these manufactures and tell them your facts on LI batteries, then get back to us and let us know, PLEASE
FAQ
Dear Mugen Power Battery user,
Thank you! We just wanted to take a moment and thank you for buying this high-quality Mugen Power battery. We truly appreciate your business and hope that you enjoy using your Mugen Power battery.
"Charging Instructions and Battery Care
To fully enjoy the enhanced hi-power capabilities, You should initialize the battery. To do so, please follow 3 easy steps:
1) CHARGE BATTERY FOR 8-12 HOURS
For the first 4-5 charges, please charge the battery in the device for 8-12 hours using the mains power adapter and with device turned on (Important: For first 4-5 charges You should charge the battery for 8-12 hours, even if Your phone is showing it is fully charged already!).
2) USE DEVICE AS NORMAL
After each charge, please use the device as normal,
until the device tells you the battery is very low, then recharge.
3) REPEAT 4-5 TIMES
Repeat this process for 4-5 times.
After that you can recharge the battery whenever is suitable for You, and just until Your device showing it is fully charged.
Important: We recommend not to try to switch on your phone if you reached 0% charge. This harms the battery, exhausts it's resource and decreases it's life cycle.
When using your device for longer periods of time (week or more) continuously on the mains power supply, please remove the battery or use the device on battery power until recharge is necessary once in 2 weeks."
and this
Q: Why is it important to initially charge the battery 4-5 times for 8-12 hours?
A: This process is needed to train the controllers in the phone and the battery to recognize new extended battery capacity. The phone needs to rewrite the capacity statistics so the correct capacity is reflected by the charge indicator. We recommend to keep an eye on the battery and if productivity declines, repeat this calibration process. More information on handling Lithium Ion batteries you can find on here at XDA forums and Battery University.