To test for a voltage leak, put a little light bulb between the positive post and the positive battery cable. If the light lights up at all, you have a circuit somewhere draining your battery The brighter bulb glows, the larger the current draw from the offending circuit. Start unplugging connectors till the bulb goes out, then start troubleshooting that circuit. A light bulb can also be used to find a shorted curcuit that keeps blowing fuses, by connecting the bulb in place of the blowing fuse.
My alarm and stereo memory and bass capacitor all draw a little current that will drain my battery over time. I disconnect it whenever it will sit for more than a couple of weeks. A couple of deep discharges will kill any battery.