A drain that will run the battery down in a few days is big enough to power a 12 volt test light. Disconnect the ground cable and connect a test light between the cable and the battery post. If there's a drain, the light will burn. Start disconnecting fuses and/or circuits one at a time until the light goes out, then trace that circuit to see what's causing the drain. Leaky diodes in an alternator can cause this type of drain, and the alternator will still do a pretty good job of keeping the battery charged up.
Jerry
