Coolgo New Laptop Battery for HP Compaq ProBook 6440b 6445b 6450b 6545b 6550b 6555b HSTNN-XB68 - 18 Months Warranty [li-ion 6-cell 4400mAh] High-Quality: Our battery choose high quality and new lithium-ion cells, safe and reliable, stable performance which can charge-discharge more than 500-800 cycles. Quality Certication: All the products pass the ISO9001, CE and ROHS, FCC multiple international authentication and completely accord with environmental protection requirement. Consummate Design: Excellent design makes the product not only has the overcharge, discharge and short circuit multiple protection, but also to balance charge-discharge of all the internal cells. Environmental Test: Standard modern assembly line. All products have passed a variety of charge-discharge and aging test before they leave the factory. 100% quality test for all items. Operation time: For standard battery(6-cell, 4400mah): 2-3 hours; for extended battery(12-cell, 8800mah): over 4 hours (Note: The actual operation time depends on how much electricity is required by the device and how you use the battery.)