High voltage in winter is normal - it is the temperature compensation kicking in. We would see 15V+ from our controller in the winter, which was actually 14V+ compensated.

Did you measure the actual battery voltage or just used the meter reading? You need to see what the actual terminal voltage is.

What battery monitor do you have? These go out of sync regularly and need to be recalibrated. It is difficult and time consuming to adjust their parameters so exquisitely that they are 100% accurate for a long time. Almost impossible, so they need to be recalibrated every so often as they drift away from true.

A load test is not a capacity test - it will not draw the battery down and there will be no need to recharge. However, if you have one of those inexpensive load testers with a resistive coil in it, you won't achieve any appreciable load with it to test a 220Ah battery. Those are OK for car batteries, but you will need a much larger carbon pile tester for that.

We have the same alternator and it will put out 40+ amps for a long time into discharged batteries. When it is down to 10A or less, the batteries are mostly charged.

13.8V is correct for that alternator. It is listed as being regulated at 14V, but we never see that. You can get replacement regulators inexpensively from Buddha autoelectric (ebay store) that charge at 14.2V. They are extremely easy to replace, and I recommend doing that (then you have a spare). Alternately, you could put a power diode in line with the sense wire. That will drop the sense voltage ~0.5V and the internal regulator will compensate up for it - giving you a 14.3V output.

Mark