I haven't bought mine yet- this review is a service. Please correct me if I'm wrong but based on comments and description I believe I am correct.
This is a snap on battery booster / extender. This will give a good battery extra life and extend time. However, if the internal battery is totally shot, this will either not work, or will only ( as a reviewer wrote) give about ten minutes additional power. If your battery is shot, buy an internal replacement battery- then get this , and it SHOULD extend battery life a great deal, as it says.