This may not be the appropriate place to post about this. If so, just ignore it, and my apologies.
Honda has a dual-mode charging system for US models. When the headlights are on, or any other combination of things that increases the amp draw through the system to a certain point, the computer tells the alernator to put out
14.4V, or thereabouts. But at all other times the alternator puts out about 12.3V. This is done to increase gas mileage.At my last oil change (2012 Civic), the dealer checked out everything, including the battery. They said the battery was ok, but was only 57% charged. It seems to me that this is a direct result of the charging algorithm. Even if the battery was fully charged, which would be a resting voltage of just under 12.7V, if the alternator is told to output only 12.3V, then the battery will be providing all the needed current until it is discharged down to that level, which should happen fairly quickly.
My understanding is that lead-acid batteries don't do well being partially charged all the time, not to mention not having as many cranking amps available as you might need. In fact, I replaced the original battery at just under three years. Yet Honda has been doing this dual-mode thing literally for decades. So perhaps I'm wrong about the effect of this system on battery life.
The odd thing is - if you want the car to charge the battery, you DO NOT want to shut off the lights, the fan, the radio, etc., because that will just lower the alternator voltage to 12.3V, which won't charge the battery at all. Instead, you want to turn on the headlights - because that will cause the alternator to put out 14.4V, which WILL charge the battery. Can you spell counterintuitive?
So one option is just to get a charger, and charge the battery overnight maybe once a week. But another alternative is to modify the current-sensing circuit so the computer thinks the lights are on even when they aren't, so the alternator will stay at 14.4V all time - just like every other car in the world does. But before going down that road, I need to be sure I understand what, if anything, this Honda system is doing to the battery because the modification, which is called the ELD bypass, is a real bear for my model car.
And in case you were wondering, it appears that this Honda system doesn't take into account at all the current charge state of the battery.
Well, I would appreciate some expert opinion on the effects of having the battery be partially charged all the time. I've read several places online that this promotes sulfation. But it's not clear. It's also not clear whether a weekly full charge would undo the sulfation.
Thanks for any advice.