After a friend removed my car radio the battery gets constantly drained and won't start, even when charged. This was confirmed with AAA.
The first thing to do is to make sure that your friend did not leave any bare wires that are touching ground and shorting out. If the wiring is ok then the problem may just be that it started to happen when the radio was removed but not a fault of your friend. The most common short will be the alternator shorted internally and will need to be replaced. A qualified mechanic can check this for shorting and killing your battery.
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