MS621FE Battery
If your DVR does not keep the date, and the time then you may need to replace the battery on the main board. It is located under the board.
The battery is a MS621FE battery. Here are some various links on the battery.
Micro Battery Product Catalogue 2008 - 2009
http://www.sii.co.jp/compo/catalog/battery_en.pdf
MS621FE Battery Spec Sheet, Data Sheet, White Paper
http://www.vaima.cn/admin/DownLoad/U...4532072231.pdf