| Some of the RF technologies used are not great for range and suffer from interference. In any case, due to the extra step of conversion needed, wireless mice tend to have a little bit more lag than wired mice. Why this is I'm not entirely sure, as wireless can be as fast as wired. The batteries do add a fair heft of weight to the mouse however!
I've not had problems with any battery related lack of performance with the Mx900 I have, but a) it's Bluetooth and tends to have a better range; and b) it gets charged every night.
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