A: First, find out your old battery part number (e.g. 'Compaq Presario V3521TU') or the model name of laptop and then match with our product compatibility table. Second, please compare your old battery with our product images to make sure their shapes are the same. Lastly, check the voltage (rating) is the same as the old one. For more details please click How to find one correct battery for my laptop?

A: There is no need to charge your new Compaq Presario V3521TU battery for 12 hours for the first time use, because lithium-ion battery is with no memory effect. So you only need to charge and discharge it normally. What’s more, you should avoid recharging it till exhausting battery power, because it will bring to much damage. Therefore you have to charge it when remaining power is nearly 10-20%. Additionally, if your battery has not been used for a long time, please charge it once a month, keep the remaining power about 40% and then store it in a dry and cool environment.

A: In general, it will not cause any damage without removing battery when the laptop connects the power supply. The battery will not be charged anymore after it is fully charged. On the contrary, it will turn to the use of power supply system. However, when your laptop has run for a long time at high speed, you’d better remove battery out of laptop due to the internal overheating.

1 Avoid Full Discharges.
2 Tweak Your Built-In Power Saving Options.
3 Disable unnecessary programs that draw energy from your notebook.
4 Adjust the brightness of your laptop display as much as possible within an acceptable range.
5 Keep your laptop and battery in a cool dry place (heat may destroy a battery).