Fake Sony Ericsson BST-33 Batteries.

The Sony Ericsson BST-33 is made in two different manufactoring facilities and two genuine batteries may look slightly different. One is high shine sliver and the other a slightly dull silver. Genuine batteries are rated at either 950mAh or 900mAh.

Fake batteries have only "Sony Eri" written on top and rated at 650mAh.
If your buying from eBay, check the listing. If the listing says either "Non OEM" or Generic, these batteries are not genuine batteries, but made by third party manufacturers to replace the BST-33.