Rega IT Replacement Laptop Battery for Compaq Presario CQ57-421SA CQ57-421SB Laptop Made from highest quality parts each Rega IT replacement Battery confirms to specifications similar and guaranteed to meet or exceed your laptop's minimum requirements. Each Battery also passes necessary authentication certifications like CE, ROHS etc. Before leaving the factory, so you can be rest assured for its quality, durability and performance. Please make sure that you are selecting the correct Battery as per you old Battery specification. Please compare your old Battery Power Rating i.e. Volts (V), Capacity (mAh) & Cells.