I thought I would give my experiences as I have a Mk2 and a MP V2.
The Mk2 does use more Battery power than the MP, and for this Machine I use 2700 mAh Nimh rechargeables. These will last for a seven and a half hour day's detecting. I have never bought a spare set as I have never needed one.
For the MP, I use 2400mAh Nimh rechargeables, and again these are fine for a seven and a half hour day's detecting.
Neither Detector has ever used up it's Batteries in the Field in this time.
Why seven and a half hours ? , well by that time I'm about to expire, even if the Batteries aren't !!.
Perhaps I should add that I use a Radio Link (Quest), to my Headphones.
Possibly this uses a bit less power than if driving Headphones direct.... ?