CWK New Replacement Laptop Notebook Battery for Compaq 510 511 610 HP Compaq 6720 6820 6830 PC HP Compaq 550 610 615 HSTNN-XB51 HSTNN-XB52 6720s 6730s 6735s 6820s 6830s 550 510 511 610 HSTNN-IB51 Condition: Brand New - Grade A cells Battery Type: Li-ion Voltage: 10.8 Volt (11.1 Volt compatible) Capacity: 5200mAh (Better than 4400mAh) 90 Day Money Back. Buy with confidence!