Eee 1005HAB PC. To get PC to operate, first must type F2 to activate BIOS and then put in correct date. After that all works well. When shut off and turned back on, need to repeat these steps. If running on battery, when we put it to "sleep", PC loses BIOS and date. If put to "sleep" while on AC power, it retains BIOS and date. Appears to be a 'weak or dead BIOS battery. Are there any instructions as how to replace the battery?