The NBMate118 external battery lasts 2-4 times longer than a new internal laptop battery (see FAQ #3). NBmate118 universal battery is suitable for 98% of the Notebook in the market. It provides two (switchable) output voltage: 16 V (works for laptops require 15 V, 16 V, 16.5 V DC input) and 19 V (works for laptops require 18 V, 18.5 V, 19 V, 19.5 V, 20 V, 21 V). The o cover most of the Notebook computers from Acer, Asus, Compaq, Dell, Fujitsu, IBM, Sony, Toshiba ... FAQ: 1.How can I find what is the voltage input of my laptop? Check the printing on the back of the mains adapter, it should clearly state something similar to 16 V 4 A. In some cases, the laptop's power input jack also print the same in addition to the polarity sign (as in Fig 1a & 2a above). 2. Do I have to remove the internal battery before connecting this external battery? No it is not necessary. However we do recommend you charge the internal battery to full before connecting this battery to maximise the running time. 3. How long can this external laptop battery last? Actual running time may vary, depending on notebook computer's configurations and what kind of applications running . This battery's capacity is 118 Wh (7375 mAh @ 16 V, 6210 mAh @ 19 V). You can compare this universal battery's capacity with your internal battery capacity to figure out how long this battery can run your notebook. For example, if your notebook internal battery out put is: 15 V & 3200 mAh; Then, your notebook internal battery capacity is 15 V x 3200 mAh = 48000 mVAh = 48 Wh; If a brand new fully charged internal battery can run 3 hours, then the NBMate118 external battery pack can theoretically last about : 118 Wh/ 48 Wh x 3 hours = 7.37 hours.