Batcap draining battery?

I bought a red top battery from the store the other day. Hooked it up and 2-3 days later AGAIN it drained the battery. It drained it so much that it killed the battery for good. The store had to give me a brand new one. So i got creative and hooked up my voltmeter to the ground and the (-) battery terminal. Just as i expected there was a drain however it wasn't just a regular drain, this thing was reading -10.6 volts. Now I couldnt really figure it out but i forgot i had a huge car audio system with a Xtant 400 farad batcap. For those of you who don't know a Batcap has about 400 cranking amps just built in to it. I didn't get a chance to unhook the batcap because it was so cold but i think its the culprit. Just to test my wierd theory i started removing fuses and the most it would drop is .2 volts. The thing is i removed the power wire (hooked up to the batcap) and it showed the battery was still draining the same ammount. A buddy of mine suggested that the although i removed the power from the battery it is still draining it off of the ground.. Do you guys concurr with this theory? Any thoughts or insight would be great! As for now, it is freezing in Houston and i will keep the battery unhooked.

I don't understand -10.6 volts from ground to the negative battery terminal. The negative battery terminal is connected to ground. If you disconnected one side of the cap, it's isolated from the electrical system.My ex once told me I have a perfect face for radio.

That is correct. But if you disconect the neg battery terminal and hook a multimeter and set it to voltage and put the lead on the battery and neg battery cable it will show you the current drain.

it will only show you the current drain if your meter is set to read amperage, not voltage.