Hi everyone,

I was wondering if anyone else have a similar experience when charging their car battery.

The car battery would be charged in the evening with an AGM capable charger, and disconnected from the car when fully charged. The 2019 RDX would sit in the garage overnight.
The charge capacity was back down to 25% when reconnected to the charger in the morning. The car battery is pretty new since it was replaced by Acura about 3 months ago.

I get the same result each time the test is repeated. I know there is parasitic drain on the car battery but I didn't think it was that much.

Does anyone know if this is a common issue with the RDX? The Acura Service Adviser doesn't seem to think this is an issue.

 

Something is wrong with your car, I dont have this issue

 

The ONLY way to determine the true “health” of an AGM battery is to disconnect it, fully charge it (make sure your charger is actually set to AGM or Gel), let it sit at least 6 hours or overnight, and then have it load tested. A battery store like Batteries Plus Bulbs will do it free of charge. This process means that you will have to remove and carry the battery there. If you are using the charger’s “state of charge” gauge or lights, that really means nothing. If it clicks off and shows Charged in an hour, no worries. If it runs and runs half a day before doing that, then there could be a problem. What charger and how many amps? Mine is 7 amps and works fine. Acura allows the Gel setting, the manual says anything under 15 volts is OK. For my charger, that is 14.7 volts.



I have a car with a nine year old aftermarket AGM battery, and an RV with four of them, and they can be frustrating to diagnose, since they don’t work like an flooded lead acid one. The chemistry is very different. Load testing is the only way.

John Davies
Spokane WA

 

Thanks for your input. I am using the Motormaster eliminator to charge the car battery.


Today, the initial charge was less than 25% (25% light was flashing) after sitting in the garage for 2 days. It took less than a hour to recharge the battery.

I will ask Acura check the battery when I take my car in for service next month.

 

How many amps?

IMHO there is probably nothing wrong with your battery. My charger does the same at first. That 25% doesn’t mean your battery is low, only that the charger is initializing and testing the battery (as much as it can). If it had STAYED at 25% for a long time, then your battery would have actually been that low. As I said, only load testing will be definitive. One reason dealers are reluctant to do intensive testing of a suspicious battery IMHO is that it is far cheaper to replace a battery than spend a lot of expensive shop labor fussing with one.

Have you looked at the manual for the charger to see if it explains the lights?

John Davies
Spokane WA

 

It really seems likely to be an internal problem with the battery. There are tests that can show that if you have the proper equipment. As we teach in automotive electrical class: There is no single test that can 100% spot a bad battery. Today's sophisticated testers run a series of tests including load testing, capacity test and a test of the condition of the plates. I know at GM we would only warranty batteries if the testing was done with an approved tester like the Midtronics. These are high dollar testers costing hundreds of dollars but are very accurate. Simple load or voltage testing will provide some data but are not complete tests on a battery's internal condition. You can drive into many auto parts businesses and they will test the battery for you on the spot, many at no charge.

 

The information below was taken from the charger instruction manual.
A. Charge Status Indicator
This battery charger has an easy-to-follow 4-LED charge status indicator: 25%, 50%,75%,100%. This
indicator provides an estimate of the battery’s state of charge as charging progresses. During charging, the
corresponding state of charge LED will be flashing. When the 100% LED lights solid (i.e., stops flashing), the
battery is fully charged and the charger has entered the Maintain stage (see Understanding the Multi-stage
Charging Process).

The charger is 7 Amps.

The battery issue reminds me of the the surface charge problem for my old car battery. When you apply a load on the battery and the charge goes right down.

 

Acura service adviser said their shop has a really good battery tester they got from Acura. I will get them to test the battery when I take my car in for service.

 

I have been closely monitoring my car battery for the last year or so. There are definitely a few quirks about the RDX battery usage. First of all, here's some general information about AGM batteries. When the battery is fully charged, the resting voltage should be around 12.7v. If the voltage is lower than 12V, you should definitely charge it. I personally charge it around 12.2-12.3v or when the auto start/stop no longer kicks in (see below for #4).

And here are the specific part about the RDX.
1) When the car is "ON" (but the engine not start), there seem to be a 0.2 voltage drop across the battery terminals. No matter what the state of the battery, there would be at least 0.2 voltage drop. If the battery is full at 12.7v, it will drop to around 12.45v. If the battery resting voltage is 12.2v, it will drop to around 12.0v. And by "ON", I mean anything electronic that is on. It could be simply opening any door (not just the driver door).

2) And if you want to measure the voltage of the battery, make sure your car is OFF for at least more then 15 min or else you will be getting a lot of confusing data because of the 0.2 voltage drop. By "OFF", I mean no dome light, no doors open/closing in the last 15 min. That means, if you want to check the battery, at the minimum, you will need to open the driver door, pop the hood, close the door, and come back in 15 min to measure, even if the RDX have been sitting there overnight.

3) When I have my battery charger hooked up to the RDX and the battery charger indicates that the battery full charged, opening any car door would cause the battery charger to restart its charging cycling. (I suspect this is what happening to the OP.) My guess is that this is due to the 0.2 voltage drop causing the charger to think the battery is no longer full. However, since the battery is still fully charged, my battery charger indicator will go back to full after a full cycling (about 40 min or so for my charger). If the battery weren't full, the charging cycling would take many hours, not just 40 min.

4) I do a lot of short city driving, so YMMV. I find the auto start/stop feature is SUPER dependent on the state of the battery. If the battery is full, the auto s/s will kick in about 2-3 mins of drive after a cold start in morning. If the battery is around 12.4-12.5, auto s/s will kick in every other light to every 3rd light or so. If the battery is lower than 12.2v, the auto s/s won't kick in at all. This is a good time to charge the battery.

For the OP, I would recommend charging the battery to full, disconnect the charger while leaving the hood opened (so you don't have to open the driver door to pop the hood). Take the initial voltage measurement after 3 hour. And then measure again the next day. If there's a significant drop in voltage (0.1v or more) then there might be some parasitic draw coming from your RDX.

Hope this helps.

 

I use CTEK battery chargers/maintainers on both my cars. On AGM batteries I found out that you do NOT attach the Neg. cable to the batteries Neg. terminal. Attaching the Neg. cable
to a dependable chassis ground nearby....a bolt through the metal of the infrastructure, etc. This came from CTEK. I have had no issues. These sophisticated battery "tenders/charger"
can be left on indefinitely. You don't need to disconnect when you think the battery is charged. LEAVE IT HOOKED UP. It's a SMART charge/maintainer to keep the battery healthy and "UP!:"

 

I haven't done any of the above nonsense.. Just start and drive normally. Has my battery ever left me stranded? No. When and if my battery dies I will just purchase a new one. Case closed.

 

This is my attitude as well. However, sadly, I am on my 2nd new car in 8 months...I don't change batteries, I change cars.

 

One comment that might help another newbie owner. Sitting in the car in the garage, in Run, trying to figure out how all the buttons and screens operate, then after thirty minutes you realize the $&@ headlights and tail lights have been on the entire time. Turn switch from Auto to Off. Lights go off. Go get charger. Continue learning all the Acura Quirks.

That is why I have a charger hooked up. For normal driving, no way.

My smart charger works perfectly with the negative cable hooked up to the battery. These AGMs are NOT vented and there is no risk of a spark causing an nasty explosion. That is why that is recommended, for lead acid ones. Or you could even hard-wire a connection for the charger.

John Davies
Spokane WA

 

That really makes no sense. I would just leave the engine running, in a ventilated area of course.

 

Same here. And I keep a booster in the car just in case. I've never needed it,, so I hope it works well..

 

You would, but I would not, it is ten degrees outside the garage. So yes, it does make lots of sense, to me. Be careful with your comments.

John Davies
Spokane WA

 

I KNOW AGM's are not vented. I was passing on the tech info from the folks at CTEK...the engineer there, and they said how to connect using the CTEK battery tender/charger!!!!!! That's them, and they
should know. This was for AGM batteries. Like it or not...I guess you are a better engineer than they are....hmmmm???
CTEK makes this charger/tender for MANY high end car makes....such as: Ferrari, Porsche, MB, new C8 Vette, and on and on. Those car co's just put their name on the front,
but, they are def. CTEK made. Mic drop!!

 

Suspect those are lawyer “Wessel words” aimed on not creating any spark, any time, any where near the battery. Reality is the smart charger is smart enough to verify polarity before actual charging starts. Some smart chargers actually do not like long cables during the testing phase on the chargers.