On some systems, pulling the battery and AC adapter, and holding down the power button will reset the CMOS. If that doesn't work, you'll need to pull the unit apart and unplug the CMOS battery from the motherboard.
This is late, but I thought I should post a response anyway. Unfortunately, A305 has the battery soldered to the motherboard. So you cannot really do anything about it without some risky operations. Use a soldering iron to melt the solder, take the battery off and then solder it back. Take care not to spill any solder outside the original area as it might short some parts of the circuit.