If you're handy with a soldering iron, or know someone who is, you may be able to "refresh" your existing battery for a lot less.
See, inside the casing of many laptop batteries lies nothing more than fairly commonplace lithium-ion batteries. You can buy replacements for the cells, swap 'em in (that's where the soldering comes in), put the casing back together, and get back to work -- all for as little as $40-50. This video provides a great example:
Obviously this requires a little bit of electrical skill, but I think it's well worth the effort (unless, of course, your laptop is under warranty and the battery qualifies for replacement).
If you have any experience performing laptop-battery surgery, hit the comments and tell your fellow readers what they should know.
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