i am writing this guide becuase i have recently been duped into buying a totally useless handgrip from a seller known as LINK-DELIGHT.
the item description claimed that it would offer more power than a conventional battery, this was not the case, it is impossible to give more power with a battery grip that only holds one cheap copy battery, or any other standard capacity battery.
after doing many hours of testing and research i found that the grip itself was a cheap chinese copy of the nikon mk-D80 handgrip that most certainly didnt live up to its expectations.( they added "L" to the name to avoid copyright issues)
i paid £58 for this item that was only worth £18 at best and had to get ebay to intervene for a refund.
my advice when buying items like this is to always read the description several times and cross reference the product on the internet on ebay and amazon etc so that you can build up a bigger picture.
a lot of chinese copies make all sorts of claims and they make it very difficult to get ebay involved as they post the items on the non uk auctions!
best idea is to look at the item and the feedback and bear in mind that most people wont complain so have your wits about you
i found out the hard way on this one but got a result eventually, but still had to wait ten days.