Best Replacement for the original Battery : 
Asus  90-OA001B1100

Compatible with model:
ASUS Eee PC 8G ( 1G RAM), 4G (512 RAM) , 4G Surf(512 RAM) and 2G Surf(256 RAM)

100% new high quality generic (non-OEM) Asus Eee PC Li-ion Battery Pack.

100% original manufacturer compatible.

No memory effect. Chargeable brand new

Chemistry: Li-ion

Volts: 7.4V

Capacity: 5500 mAh