Fitted the T520 with a slice battery. The laptop is then put into sleep mode with slice battery at 8% and laptop battery at 80% charge. I booted up the system and found that the power had been lost and the machine is booted up from cold mode, causing me to lose previous documents / windows opened before the laptop went into sleep mode.
Issue has been solved via updating the BIOS and Power Manager. Follow the links provided below to update the driver