"if you have to ask, you can't afford it" LOL... sorry. (had to say it) /sarcasm
new batteries are expensive... if your laptop is a "cheap" one it probably is not worth it.
i would estimate 200 dollarsfr a new battery. (and if your laptop is not popular you might be SOL)
if you have an Apple laptop you would be in better shape because they have Apple standing behind their products.
BTW, system information is very useful in this case...