always empty battery

My motor don't charge the battery ...... mercury 60 hp 2006 bigfoot .... i want to know what kind of test i should do to be able to know the defect part .... thanks in advance

Easy test- start with a fully charged battery. Use your voltmeter at the battery terminals- with the engine off, any reading below 12.1 VDC indicates that your battery should probably be replaced. With the outboard running at idle, you should see a slight increase in voltage, usually in the 12.5 - 12.9 VDC range. As you increase the engine rpms, the voltage should rise, but no higher than 14.9 VDC. Readings out of these specs indicate either a faulty stator or regulator/rectifier, most likely the regulator/rectifier.

Mercury had a major problem in the mid 2000s with regulator failure on their mid-sized outboards. The regulators where poorly positioned on the water jacket and did not receive sufficient cooling, causing regulator failure (and even wiring fires). There was a major "fix campaign", which included a new regulator, and a newly designed water jacket cover to mount the regulator in a cooler position. The easiest way to tell if your outboard had these repairs- if the charge (red) wire from the regulator has an inline fuse, the repair has been done, if there is no fuse, then it hasn't.

If you post your serial#, I'll see if your outboard was onne of those affected by this problem, and forward you the service bulletin, which more fully explains the problem, and gives the part numbers and procedure for the repair.