I'm not positive of the math, but given my own experiences it might not actually be totally unreasonable. My XBox controllers burn through rechargeable batteries pretty effectively. Not in the "I have to replace these with a freshly recharged pair" sense, but in the "these batteries can not be recharged anymore" sense. I have 8 2-year old batteries that will no longer hold enough charge to get 20 minutes of play time.
If the XBox is getting used enough, and if you don't have a great coupon for rechargeable batteries, it's probably worth at least considering.