My 3 yr old battery went dead and would not jump off. Replaced it. After 48 hours it was dead. Jumped it off. Held charge another 10 hrs. Dead again. Took to a shop. They replaced the negative cable end. Went to pick it up 3 hrs later it was dead. After they checked the battery. Said my new battery was no good. Went and got a new one. Another 48 hours and it's dead again. 2005 Ford Focus. Any suggestions?
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.