New battery dead after 48 hours

Doing a parasitic drain test is quite simple, all you need is your multimeter (DMM).

Remember to place your DMM lead to 'A' and 'COM' , use flat screwdriver to close the latch on your bonnet, shut all doors and wait for about 30 min. for the vehicle to go fully into sleep.

If you see high current draw, let say 800 mA, start pulling all the fuses one by one and watch any for any difference. If you pull a fuse that will drop the current to near 0 mA you have isolated the problem.

If neither fuse makes a difference, disconnect the heavy red cable leading to your alternator. A bad alternator diode will allow current to flow from the battery to the alternator when your engine is shut off. The winding in alternator will just sit there and draw current like a stalled electric motor causing a drain.

Alternators are not always fused, they will usually have fusible link only and thus not revealed problem when pulling fuses.

Hope that helps.

DO NOT start the car with this test in place starter current would fry your ammeter.

Many years ago I had a similar problem, it turned out to be the boot light was staying on causing a small current drain.

A very helpful garage mechanic climbed in the boot to find it.