I have an ASUS K42JR laptop, and the battery life in this thing sucks (2 hours max). I'd like to get a bigger battery for it, and I've found a bunch online, but I have no idea which one fits/works with my laptop.
Any idea how I can find that out?
Most places where they sell batteries online tell you which models they support. You typically search by manufacturer and model. Also if you go to a local store that sells batteries such as Batteries Plus you can bring them your laptop and they will be able to find the proper battery.
However I actually don't believe that Asus makes a extended battery for this laptop. All of the websites I visited only sell the standard 6 cell 4400 mAh battery. An extended battery for a laptop of this size would be a 8 or 9 cell battery with around 5600 mAh.
You can also ask Asus directly by filling out a Technical Inquiry From http://support.asus.com/techserv/techserv.aspx to see if they make an extended battery for your laptop.
There should be an indication of which laptops the battery will fit on the site. If you post some links that would help.
The things to check are:
a) it has the same connection as your current battery
Having said that, there are some laptops that can accept an external battery and I've known of cases where you could replace the optical drive with another battery. You will need to check your laptop's specs to see if either of these apply.
Thanks quack for reminding me about these cases