Question concerns my 2007 Pacifica, I installed a new AGM battery last winter and I check on it periodically because this car doesn't get driven frequently. Lately I'm finding it at 12.2V to 12.4V after only sitting for a day or two after being fully charged (via a long trip/extended use over a few days). Even after being on a charger (and I've tried several) till it charges completely, after a few hours the battery settles down to 12.4V, which equates to somewhere around 50% state of charge.
I checked alternator voltage and it's about 14.4V when the vehicle is started. I drove it to work and back (35 miles each way) for a few days just to simulate daily driving conditions. After that 35 mile drive home (and battery presumably at full charge), the alternator is putting out about 14.3V. Shut it off and a few hours rest (for surface charge to dissipate) and battery is back down to 12.4V. This occurs even if the battery is removed from the vehicle, so it can't be attributed to excessive parasitic current draw (which has never been an issue with this car).
That resting voltage seems awfully low to me for a 1 year old AGM battery. When new it would hang around 12.7-12.8 even after a week or more of the car sitting. I know from plenty of research on AGMs that they prefer a charge/absorption voltage of up to 14.6V, but float voltage should be maintained at 13.2-13.8V, which is actually lower than a flooded battery.. The fact that my alternator is still putting out 14.3V after a long drive (and at idle nonetheless) makes me wonder if it's overcharging, and whether a steady 14.3+ volts at all times is normal. Of all the vehicles I've owned that I can recall charging voltage being at (after a long drive) were always 13.7-13.8V. Over 14 volts with battery at full charge seems unusually high to me.
I've always put the battery on an AGM-compatible maintainer anytime the car isn't going to be driven for awhile, so I don't think maintenance is an issue. I also see some acid residue starting to build up around the battery terminals, something I've never experienced before and don't think is normal for an AGM. Only possible cause for a weak battery after one year I can come up with is overcharging. I'm thinking of picking up a junkyard alternator just to compare voltage characteristics... alternator replacement is about a 5 minute job on this vehicle, so might be worth it just for giggles. If 14.3V is normal for a charging system at all times and at idle I'll just abandon the idea of using an AGM and go back to flooded.
Curious what you folks think....
I checked alternator voltage and it's about 14.4V when the vehicle is started. I drove it to work and back (35 miles each way) for a few days just to simulate daily driving conditions. After that 35 mile drive home (and battery presumably at full charge), the alternator is putting out about 14.3V. Shut it off and a few hours rest (for surface charge to dissipate) and battery is back down to 12.4V. This occurs even if the battery is removed from the vehicle, so it can't be attributed to excessive parasitic current draw (which has never been an issue with this car).
That resting voltage seems awfully low to me for a 1 year old AGM battery. When new it would hang around 12.7-12.8 even after a week or more of the car sitting. I know from plenty of research on AGMs that they prefer a charge/absorption voltage of up to 14.6V, but float voltage should be maintained at 13.2-13.8V, which is actually lower than a flooded battery.. The fact that my alternator is still putting out 14.3V after a long drive (and at idle nonetheless) makes me wonder if it's overcharging, and whether a steady 14.3+ volts at all times is normal. Of all the vehicles I've owned that I can recall charging voltage being at (after a long drive) were always 13.7-13.8V. Over 14 volts with battery at full charge seems unusually high to me.
I've always put the battery on an AGM-compatible maintainer anytime the car isn't going to be driven for awhile, so I don't think maintenance is an issue. I also see some acid residue starting to build up around the battery terminals, something I've never experienced before and don't think is normal for an AGM. Only possible cause for a weak battery after one year I can come up with is overcharging. I'm thinking of picking up a junkyard alternator just to compare voltage characteristics... alternator replacement is about a 5 minute job on this vehicle, so might be worth it just for giggles. If 14.3V is normal for a charging system at all times and at idle I'll just abandon the idea of using an AGM and go back to flooded.
Curious what you folks think....
