Battery going too quick

[RUQ1KA]

(dont know if this is the right place to post it but here goes)

Ok heres the problem

The belts in my EB have started squealing so i decided to leave it sitting in the yard till i have time to work on it

Last time i drove it was Wednesday? I think
since then its been sitting in the yard until monday when i went to start it and the battery was completly dead! i mean not even central locking worked or the interior lamps!

So what could be causing this?
I have put a TV/DVD system in and a pioneer head unit but it doesnt seem to be causing the problem from what i know

I put the stereo system in the day after i got it so i'm unsure if it had this problem from when i bought it, and it was being driven as a daily at that time so it didnt have time to run out

I had the same problem where the battery went dead when i was doing the head gasket in it back a few weeks ago

So could there be something draining the battery that i dont know about?
or could it be the battery it's self thats gone?

The dvd system is connected to the cigarete lighter so it cuts off power to it when the cars off so i highly doubt that would be causing the problem

Anyway thanks in advance for your help