Thanks. Good advice.

Another name for AGM is SLA, since they can't easily spill their contents (acid).

 

Mister Bill: I found this article from Interstate Battery. It may explain why your AGM batter went belly up in short order.
https://www.interstatebatteries.com/blog/how-to-charge-an-agm-battery

 

Another name for AGM is SLA, since they can't easily spill their contents (acid).

But not all SLA's (Sealed Lead Acid) are AGM's (Absorbed Glass Mat).
An AGM is a type of SLA.
SLA's can also be flooded or gel types.

 

Mister Bill: I found this article from Interstate Battery. It may explain why your AGM batter went belly up in short order.

That article says a lot but parts of it make no sense at all. It talks about "Sending more amps " into the AGM battery but with a lower voltage. Most simple 6 amp chargers have a voltage drop as the current increases, so that at a higher current the voltage is less.

An automotive charging system replenishes the charge while the engine is running, often not for eight hours. The article carefully does not specify the different voltage and current requirements of the AGM battery, It ONLY states to use "the correct charger" while not giving one word as to what voltage and current level makes a charger correct.
At least I did not see any specific details. Did I miss them??

 

Mister Bill: I found this article from Interstate Battery. It may explain why your AGM batter went belly up in short order.
https://www.interstatebatteries.com/blog/how-to-charge-an-agm-battery

More marketing than battery science, imo.

 

I have a 4 amp battery charger - a Smart Charger. It boosts the voltage then drops back to see how the battery is holding the charge. One of those high frequency battery fixer (please don't ask me to explain that, it is supposed to heal sick batteries).

Before installing the batteries into the cars I put then on the charger. It topped them off in 30 minutes and never exceeded 14.4 volts. More time was spent at lower voltages like 13.8.

 

At what current level did that "4 amp smart charger" top[ off the batteries??? That does matter! Both voltage and current need to be known to understand what is happening, and what condition the battery is in.

 

Trying to figure out if I should replace my battery. It's in a 2017 Rav4 and the battery is original equipment. The battery voltage was read after the car sat over night. When I started the car the voltage went up to 13.8 volts. I think that's normal when running. I haven't checked the voltage since shutting it off as I figure it'll just be high due to having just been charged.

Every first Saturday of the month I do an overall health check in the engine compartment. Oil, coolant, brake fluid, battery voltage not just after having driven the car so as to not get a false reading. Last month it was, if I recall, 12.08V.

Since the battery is 9 years old and given the reading, should I consider changing it before I get stuck?

Oh, and only one cell was a little low on water. Not showing the battery plates. Never the less I topped it off with distilled water. My dad uses distilled water in his CPAP. TMI?

A charged car battery should always read above 12v with engine off, period. Just go to a O'Reilly's or some place like that, they will test the battery (they don't just measure voltage either) for free. I live in Arizona and if I get 3 years I'm happy. When your battery does fail it will fail suddenly not gradually, that's been my experience, you'll turn the key and - nothing will happen.

 

At what current level did that "4 amp smart charger" top[ off the batteries??? That does matter! Both voltage and current need to be known to understand what is happening, and what condition the battery is in.

Went looking for the charger I have but couldn't find one to link to. I will have to take a picture of it. But it doesn't tell me the amperage. It shows a battery with 5 bars. As the state of charge (SoC) increases so does the number of steady bars. Meanwhile, 1 or 2 bars will be flashing showing that it's in that range. The charger will switch on and off showing SoC and the voltage being pumped into the battery, back and forth until the battery is nearly fully charged. I'll get a picture later today.

A charged car battery should always read above 12v with engine off, period. Just go to a O'Reilly's or some place like that, they will test the battery (they don't just measure voltage either) for free. I live in Arizona and if I get 3 years I'm happy.

The two new batteries came with the following voltages: 12.60 and 12.67. So they were at the expected voltage of 12.6 or higher. I haven't looked at the batteries today, after batteries have had a chance to rest. When I grab a picture of the charger I'll also read the resting voltage and report back. This morning I have an eye doctor visit, so it won't be right away.

When your battery does fail it will fail suddenly not gradually, that's been my experience, you'll turn the key and - nothing will happen.

My experience with sudden death batteries was with the DieHard brand. And it was my opinion that - yes, they DO "DieHard" and fast.

All my driving life I have had wet cell batteries. Perhaps on an occasion or two a family member has had a maintenance free battery, and I think it was DieHard.

After installing the batteries in both cars I started each. I noticed a distinct difference in the way the car started. It started quick and almost immediately. Funny, with the old batteries you gradually get used to the drop-off of starting power. You don't realize just how hard it is to start on an older battery until you put a new battery into service.

This is an amazing website. I think I'm going to enjoy being a part of it. Thanks for all the great input.

 

OK, here's the promised picture. Tried to find a link to the same thing or something similar but couldn't find one. Seems the newer models are up to 6 amp charging capability.

 

No sooner than I say I can't find it - I found it. But it looks like they changed the labeling just a bit. Still, it's the same one as I have.
https://www.amazon.com/Automatic-Mi...y-Charger-Maintainer/dp/B0CCY61JP4/ref=sr_1_6

 

Here's a better link and more accurate. But in the description it says the same thing as the other link.

https://www.harborfreight.com/4-amp...ntrolled-battery-chargermaintainer-63350.html

 

Quite an interesting ad! But not much real information except "six volt and 12 volt" battery types. It is more descriptive and honest than a lot of product descriptions.

 

It addresses your concern about being capable of charging AGM batteries. If you've looked at the links and followed them down far enough you'd have found that AGM is a part of its programming. Now, if the CAR is capable of not overcharging an AGM, the system should be just fine. I've seen those dumb chargers (transformer / rectifier) produce voltages as high as 17 volts, yes, that would be the death of any battery designed as a 12 volt battery.

 

It addresses your concern about being capable of charging AGM batteries. If you've looked at the links and followed them down far enough you'd have found that AGM is a part of its programming. Now, if the CAR is capable of not overcharging an AGM, the system should be just fine. I've seen those dumb chargers (transformer / rectifier) produce voltages as high as 17 volts, yes, that would be the death of any battery designed as a 12 volt battery.

I have a similar charger, it has several modes, slow, fast etc. The slow takes longer but impacts battery life less.

 

Modifying a car's charging system is not likely to be a good idea because on modern cars there are a whole lot of things that draw quite a bit of ccurrent, and really run off the alternator. So that any change to the vehicle electrical system will not be a small change.

 

Back when I was driving a 72 mustang I installed a switch that would cut off rotor voltage causing the alternator to have no output, therefore no load on the engine. I did some racing and that was the reason for shutting the alternator off. Later I rigged it so that when I step on the brake pedal the alternator would automatically re-engage and charge the battery. But under normal driving the alternator was always switched on. But I'm not thinking or planning on any modifications. All I wanted to know was what the battery voltage at rest was telling me. That question has been addressed. Batteries have been changed. The project is finished.

I must say there's a lot of talent here. Thank you all for your input.

 

Been reviewing comments and want to address unanswered questions:

How far do you drive it each day (or each time you start it?)

Typical yearly drive is about 12,000 miles. More than just daily commute to work and back.

I've also heard people who park close to their house, the car can still read the RF keyfob and thinks you are near, so it does not put the BCM to sleep mode as it should, and extra parasite drain occurs.

Interesting thought. The garage is detached and the living room or bedroom are far enough that I can't lock or unlock the car. The kitchen is another story. As for whether I can lock the car when the steel garage door is closed - I'd have to have someone in the garage who can tell me how it responds to the FOB.

For what it's worth, I don't think I have a parasitic draw. I should have checked the resting voltage before starting the car but I just wanted to get off to work. Tomorrow I'm off. I work four 10's then off three days then five 9's then off two days. Makes planning for weekends a bit troublesome.

 

@Prariemystic: Certainly there are both incorrect theories and total lies spewing out over the internet. Consider that assertion about the key fobs to be simply A BIG LIE! All sorts of stuff gets made up, by those with nothing better to do.

For battery voltages, anything below 12.0 volts indicates a state of discharge. Not total, but certainly quite a bit below 100%

 

When your battery does fail it will fail suddenly not gradually, that's been my experience, you'll turn the key and - nothing will happen.

Had that happen to me when I stopped at a gas station.
When I was through filling the tank, turning the key to start just gave a click.
Fortunately, I was able to get a jump, and then replaced the battery after I got back home.