The Madvapes 4.8v battery is NIMH, and only rated at 600 mah; not a whole lot. They are 4 pretty small NIMH cells in series. Takes a special charger, too. I would expect such a small cell to definitely suffer a voltage drop while vaping. The Madvapes VV box mod is pretty cheap, and will give you a constant voltage. I built a box mod with Madvapes parts, and it works really well; lasts me all day. During the day when I want a harder hit, I can simply turn it up a little. The box is well worth the price. Would recommend a voltmeter for checking the voltage, though. I have noticed that when I set the voltage output on mine, even when vaping there is NO voltage drop; in fact, it actually increases about .01 volt!