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2009 Hyundai Accent - Battery drain

I have taken both alternator and battery to have tested,both are good! But battery keeps draining after I run it for awhile,no lights are on,no stereo was installed. What else could it be?

When you had those tested, were they out of the car ?

It could be a fuse

Check the fuse box under the hood, there should be one marked “ALT” or Alternator" or “BAT” or Battery"
Should be about a 100 amp fuse.

After an electrical system repair the standard test is to make sure the system is operating as designed. So start the car and monitor the voltage across the battery. The voltage should rise from 12.0 to 14.5 over a few minutes. If not you have a disconnect between the alternator and the battery i.e a bad connection. With the engine running measure the voltage between the alternator B+ terminal and the battery. It should be 0.

My standard battery/alternator first check is to measure the battery voltage before first start of the day. Should be about 12.6 volts. Immediately after starting the engine, 13.5-15.5 volts. What do you get?

If you tested the alternator while it was out of the car then most likely there is a problem in the wiring to the alternator. Does the battery warning light turn on when you turn the key from OFF to the RUN position? If not, then the field wire needs to be checked out. It supplies power to field windings of the alternator.