Issues with charging dual AGM batteries to 14.7v

Hello all I have a dual battery set up from Genisis with 2 yellow top group 34 Optimas. I also have a tune to charge the AGM batteries to 14.7 volts. It pops up on my voltage meter as 14.7, that is until my vehicle is shut off it drops down to 13v immediately. Then eventually to the factory charge setting of 12.7v. Anyone know why it wont hold the batteries at 14v? I know the genisis system isolates batteries at certain volts so I'm not sure if its not allowing it to fully charge both batteries to 14.7.

any intel on the would be much appreciated.

 

Usually you never want to go above 14.4v for charging. But when charging the voltage output of the charging system is normally higher and that's what your voltmeter will show when charging. For a 12v AGM battery the resting voltage is 12.7-13v for fully charged. Voltage will always be higher immediately after charging but will trickle down to the resting voltage in time.

 

So is the point of the alternator charging to 14.7 just to charge the battery faster? Optima states a max of 15v charge with an alternator.

So technically this has nothing to do with how much charge the battery holds?

 

Check out this article. Good info.

 

Thanks for the info

 

I’ve never heard of the concept of charging a battery to a voltage. Charging a battery is a process of storing energy in the battery and voltage is not the same as energy. However, I think it is typical for the battery voltage to vary slightly based on how much it is charged.

I’m not sure about other batteries, but automotive batteries are typically charged at a voltage that is higher than the voltage they naturally have. If you put a voltmeter on your battery, it will read about 12v when the engine is not running and about 14v when it is running (assuming your alternator is working). That’s how one typically diagnoses a good/bad alternator.

 

An excellent post here if you all want to nerd out on basic electronics.

If you have a scan.gauge II or an OBDII app / reader you will see battery voltage. Think of voltage like water pressure - it is what pushes electrons through a conductor. Voltage is a unit of current in a battery so I can roughly tell how much charge I have in my two lead acid trailer batteries just by monitoring the output voltage. Charging a battery requires forcing surplus electrons toward the half of the battery that is the anode. This is why your charging voltage will be higher than what you read on the battery with your voltmeter when the car is off. AGM, Lithium, and Lead Acid batteries have different charging tolerances because of their different characteristics (chemical makeup, vented vs. not vented, etc.). You wouldn't run city water at 90 psi through your drip irrigation system because that would be forcing fluid through your drip pipes at pressures it is not capable of handling. Same thing with charging voltages and batteries; different batteries can only take so much pressure (voltage forcing surplus electrons to the anode).

AGM, or Absorbed Glass Matt is a type of sealed, lead-acid battery. An individual lead-acid battery “cell” is generally 2.20–2.30 volts. In order to get a desired voltage, manufacturers design a single module (or “jar”) to hold the cells together (in series). For a 6 cell jar they will put six cells together in series. The “fully charged” voltage will be 13.2–13.8 Volts DC (AGM). There is some variance, but that gets you in the ballpark. The battery will be marked with its recommend charge voltage. Each battery model will have a spec sheet available on the manufacturer’s website.

13.2 is a good ballpark figure for where an AGM battery should be at full charge (it varies though -- 13.2 - 13.8). Remember that your alternator is handling the electrical load of your Taco when running and the 14.7 volts you have set is the charging voltage -- the alternator sending excess electrons to the cell anodes. That you charge at 14.7V does not mean the battery should be at 14.7V when it is off and you are checking the battery with a meter. Check the spec sheet from your battery manufacturer to be sure what your specific AGM should read at full charge.

 

Voltage = pressure to push current through a load or resistance.
Current= Actual power in electricity measured in amps.
Resistance= resistance to the flow of electricity through a conductor or load.

When you talk about voltage it is not an absolute ( I have a charging voltage of 14.7v)
You must consider the current the alternator is producing.....say 30 amps. Note: 30 amps is a random number I chose for discussion.

So to recharge your battery it takes 14.7V to push 30 amps of current through a conductor (resistance) to charge a battery.

The 14.7v you are reading is the voltage needed to push the current, 30amps ,through a conductor or a resistance.

when the vehicle is shut off the alternator is no longer charging. The 13v you see right after the car is shut off is a surface charge.

It eventually settles on 12.7 due to the number of volts per cell in the battery.

 

This is extremely helpful thank you

 

Thank you for the info. This was very helpful