Are your batteries fresh? They claim it to be pretty fast:
And it's fast too: the Battery Extender takes your device from zero to 45% charged in just 20 minutes!
And what do you mean by it doesn't have enough juice to run? If you got a charge screen, it's running, innit? Does the charge icon show a lightning bolt or a power plug? If it's a power plug, your AA's are too dead to charge the phone anymore.