Actually I just disconnected the amp last week because of the power drain (the biggest battery I have is 4200 mAh NiMH). I noticed no real difference whatsoever in the volume I normally use, which is pretty loud when outside. I'm using a Visation speaker and I would get brownouts on the DBC after 12-15 minutes of hard driving with that battery. Once I disconnected the amp, I went well over 35 minutes without a brownout when I stopped and the battery had plenty of juice left.
I'll use the amp when I want to hear Merlins (or is it Packards?) across the lake in the Vospers, but for engine and battle sounds in tanks, the Benedini does just fine on it's own.

I ordered the amp when I first hooked up the StuG and was drowned out by all the Tamiyas on the battlefield. So I put in the amp and a better speaker, but in actuality, the amp wasn't being used much, the speaker itself made all the difference.