This is a high-performance replacement laptop battery for the Sony VAIO VGN-SZ491N/X, guaranteed to meet or exceed the OEM specifications of your original. The laptop battery is 8.13 x 1.94 x 0.76 inches with an output of 11.1 volts. The chemistry is Li-Ion at 4400mAH capacity. Manufactured by Empire Scientific, model number LTLI-9038-4.4. We offer a 1 Year Warranty with purchase. See this product elsewhere at a lower price? Call or email us; we have a Price Match Guarantee.