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Noticed that the battery voltage on our 2109 RDX was sitting kinda low (12.3V) after the vehicle hadn't been driven in 24 hours, so I put that battery on my CTEK smart charger and even ran the desulfation mode. Over the next two weeks I monintored the battery volrage and came to the conclusion that the car's charging system is working properly, but the battery itself just doesn't hold a charge very well. My fancy electronic battery tested showed the battery to have good CCA and relatively low internal resistance, so other than the low charge thing, the battery tested just fine. But I figured I'd replace the battery just for the hell of it, so I went to Costco and purchased the recommended AGM battery for the RDX, which has an even higher CCA rating than the factory battery.
That was about two weeks ago. Yesterday, I checked the voltage of the new battery after the RDX sat in the garage overnight and it was 12.3V.
WTF? Has anyone else noticed low battery voltage on their RDX? I'm guessing not too many people check that kind of thing, but figured maybe some of you have. The vehicle doesn't seem to have any parasitic draw issues or anything like that, so I'm at a loss here. Do AGM batteries tend to shed a small amount of voltage and sit at ~12.3V after a while? It doesn't ever seem to get any lower than that. But at the same time, an AGM battery at full charge should be 12.7V. Our new battery, at 12.3V, is around a 60% state of charge. Very strange....
Outside of the 'low' voltage, any issues with starting or electronics? If not, don't worry about it.
No issues at all. But don't tell me not to worry about it. I'm trying to figure out WHY it's happening. Having a battery (especially a new one) at a low state of charge could be an issue if a family member ends up in a vehicle that doesn't start. Just because there hasn't been an issue yet doesn't mean that it can't happen.
No issues at all. But don't tell me not to worry about it. I'm trying to figure out WHY it's happening. Having a battery (especially a new one) at a low state of charge could be an issue if a family member ends up in a vehicle that doesn't start. Just because there hasn't been an issue yet doesn't mean that it can't happen.
Normal resting voltage is 12.6 volts. You're not that far off. If the battery is measuring 13.7V or so with the engine running, don't worry about it
First thing would be use another volt meter and compare the values. Couple of tenths differences are very common.
My 2021 with 21k miles often tests at around 12.4 volts standing voltage even after a few hours of use. . While not tested often it passes the load test 650 CCA spec at 800 CCA.
Most modern vehicles in the last 5-7 years have a battery charging management system that are not in sync with those AGM resting voltage specs. That charger manager is not like the old days when max charge was used 100% of the time. Charging management voltages can be 12.6 -15.2 volts while the engine is running. The days charging voltages of 13.8-14.2 with no variance are also gone. Battery charge management also carefully manages charge by temperature.
As long as the battery passes the load capacity test…….early battery replacement is pointless. Looking for problem that has no symptoms and is similar to other known good batteries …well you can draw your on conclusions. If you ask the dealer to warranty replace ……they will use the CCA capacity test as the determining factor. Warranty claims submitted require those battery test values to be on the work order and warranty claim.
Also if the idle stop system is still active……..then the system is “happy enough” to allow no charging while stopped.
🤔Last shop around and find a better chart 😂😂😂😂🤯🤯🤯🤯🤯 as the values on the charts vary.
I would say 12.3 for a resting AGM isn’t really abnormal, a fully charged AGM will sit about 12.5-12.6 or so. Overcharging a battery especially an AGM will damage it, they work a bit differently then your standard lead acid batteries, I used to run huge car audio systems with multiple XS Power batteries and it wasn’t abnormal for it to rest at 12.3-12.4ish. To really get a true value of it resting you would want to take it out, fully charge it with an AGM specific charger, let it rest for a bit, several hours and then check the voltage. High voltage kills AGMs, most want to charge at 14.4 at most, some people would charge up with 14.6-14.8 for quicker charging but it’s hard on them.
i believe, not 100%, but if I remember correctly that fully charging a battery puts more wear on it and also uses more energy, aka fuel, so these modern cars do not really ever fully charge them. It makes them last longer overall, more years out of them, and saves fuel by not putting as much load on the alternator. AGMs have plenty of capacity to start the car many many times even at a 50-70% charge. Typically when it’s colder out, winter, you will see the charging voltage be higher then in the summer
heat is another major killer of batteries, you will even notice air ducting for cooling them in the RDX, especially AGMs are damaged by high heat, also charging to a higher capacity while under high heat would cause more damage, the car most likely is trying to make the battery last as long as possible by monitoring temps and voltage
i believe, not 100%, but if I remember correctly that fully charging a battery puts more wear on it and also uses more energy, aka fuel, so these modern cars do not really ever fully charge them. It makes them last longer overall, more years out of them, and saves fuel by not putting as much load on the alternator. AGMs have plenty of capacity to start the car many many times even at a 50-70% charge. Typically when it’s colder out, winter, you will see the charging voltage be higher then in the summer
80% is the usual charge unless you really need all the capacity. The last 20% takes a lot longer and is harder on the battery long-term.
06-13-2022, 11:41 AM
