Sometimes there isn't anything more frustrating than getting ready to take a photograph only to realize your battery is dead or missing. Your Minolta camera is susceptable to these problems because it has a removable battery and the battery is lithium-ion based.
Lithium-Ion based batteries won't hold charges forever; they eventually wear out. Detachable batteries are easy to lose. This Synergy replaceable battery for the Minolta NP-400 is a great solution to fix these problems or just to have an extra battery around for those times when you get into a serious large quantity photo-taking mood.