The fixed phrases take long and last long (with long *only*, as opposed to quantified time expressions like so long, as long, that long, two hours, all day, etc.) are Negative Polarity Items.
This means take long is in fact not grammatical outside the scope of a semantic negative. The last example sentence in Tolerance72's answer is grammatical with take long because of the negative; all the other examples in answers (so far, anyway) don't use this fixed phrase.
So *Some battles take long to win is ungrammatical.
There are a lot of NPIs and they have different properties -- they're idiomatic as hell. In particular, last long requires a fairly strong negative field, especially when separated from the negative element.
For instance, only, would rather, and doubt are all negative triggers, but only doubt can trigger the NPI take long (the first three below are ungrammatical), and then only in the last sentence, where it's contained in a negatively-entailed clause (i.e, Bill doesn't believe it took long):
- *Only Bill thinks it’ll take long.
- *He would rather forget about it than take long.
- *She doubts Bill's claim that it took long.
- She doubts that Bill believes it took long.
More examples of this phenomenon are available in this puzzle, and this encyclopedia article covers the subject broadly but briefly.
Executive Summary: When a word or phrase sounds funny like this, check for NPIs.