power battery grips?
 

Has anyone tried the Zeikos power battery grip?

Zeikos | ZE-CBG5DII Power Battery Grip | ZE-CBG5DII | B&H Photo

It seems to have he same features as Canon's battery grip at a 1/4 of the price.

I got an even cheaper one from China, off eBay -- and they even included two batteries. Works perfectly.

-- peer

I haven't bought it, but I do have my eye on it... although If I can wait I'll probably get the Canon since I know the Canon will work perfectly everytime.

I've just bought another grip. Apart from the extra power for filming and better control for vertical stills, The 5D power grip also helps lift the camera body to centralise the lens in my underwater housing.

I've not had any problems using extra non-Canon batteries, except that they do not provide full battery indication on the 5D LCD display. The 5D does warn you of a low battery when they are almost depleted, but at least the Canon original batteries provide a decent indication of how much power is left.
Another thing to note is that if you are working in Canon EOS Utility the screen indicator will show that your battery level is low, even on a full charge, so you can simply ignore the red "Battery Low" warning if you've just placed a freshly-charged non-Canon battery in the chamber.