li-ion 9 volts batteries

[alidav]

Can you suggest some alternative 9 volts rechargeable batteries to ipowers, the  li-ions are much less expensive, they give 8.4 volts when fully charged ( as the i powers )and are up to 800 mah, why still seems there is nothing to use than the ipowers? i have read the lectro faq  about that but is quite old and don't consider these new li-ions much more effective.