Bearing in mind many cars will either be sitting idle at this time, or will only be used for relatively short journeys, I think it may be very valuable to be aware of the way a Jazz battery is charged by the alternator.
It seems that to charge the battery, if you are going on only short journeys, the car needs to be run with either the headlights or the heated rear window on!
Otherwise, the alternator will not charge the battery and after successive short journeys there is major risk of a flat battery.
Also, if the car is not used for a couple of weeks and/ or is then used for only short journeys the battery will go flat through lack of charge from the alternator.
So it seems best to use the car regularly with the head lights or heated rear window on (i.e. a high current drain) unless you can use a smart charger on the car whilst it is parked up.
Otherwise in a couple of weeks or so there will be a lot of flat batteries around.
Sounds counter intuitive.
Jocko's post below sets out the principle.
Perhaps someone can explain this better than I have.
Found this interesting post:
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.
Not all appropriate, but may explain some battery issues some Jazz owners report.
