[DannoXYZ]

Battery tester will just say you've got drained battery, but will tell you no useful information as to why. Measure actual drain amount:

1. Set voltmeter to 0-10 amp range
2. Disconnect negative battery cable
3. Connect negative lead of voltmeter to negative terminal of battery
4. Connect positive lead of voltmeter to negative battery cable
(use test-cables with alligator clips for hands-free in #3 & 4)

What is current flow from battery? By inserting voltmeter in-line with battery circuit, any and ALL flow must go through meter and can be measured precisely.

5. Disconnect fuses one-by-one and see which circuit causes drain to stop

6. Inspect all wires and components of offending circuit from end-to-end for frayed exposed wires which may be shorting

One very common source of drain is the dome-light wires where it goes across the top of windshield.