Aux Batteries keep dying

The Optima's don't have a very good reputation.

Check your charging voltage again.
13.8 really isn't enough under most circumstances.

The heat in Arizona tends to be hard on batteries......but not THAT hard.

 

^^^^^^^^^^^

What Sam said.

 

sounds like your good, but i would charge it up. a new battery should be around 13v

 

Are you driving far enough per trip to keep it charged? If not, it'll gradually get lower and lower.

 

There should be no more than a 0.5A drain with the key in the house, all doors closed and the vehicle "fully off". I find that add-on stuff, from usb chargers in hot-at-all-times sockets, to stereo equipment or other stuff can kill a battery in a few days of sitting.

 

AND.....13.9 is just barely enough to keep an AGM battery charged if full to start with.
I don't KNOW that it should be higher than that but I strongly suspect it.......since your 12.6 is NOT fully charged for and AGM.

 

Even 0.5 Amp drain will drain the battery in a few days. The 'off' drain needs to be far lower than that.

Does the Gen2 even have an always-on 12V socket? My Gen3 socket is automatically turned off.

 

After 40 mins in the state described by 05PreeUs, the quiesced draw should be 20-50 mA

A brand new AGM battery should have a resting voltage of ~13.2 V after charging. An AGM charger will charge at between 13.7 and 14.4 V (depending on the stage of charge and the battery's SoC) to achieve that. Immediately you remove the charger after charging it will be ~13.7 V, but this (surface charge) will quickly bleed off within 10-15 min to settle at its resting voltage. A brand new battery should always be fully charged before being put into service to check this.

I would do a further investigation of your issues to confirm whether the battery is faulty or you have a parasitic draw.

 

Which is typical of most "mechanics" who really know little to nothing about electronics.
An AGM battery at 12.6 is only about 75% charged.
A wet cell battery requires about a tenth of a volt per cell extra for a good float voltage......so 13.2 total.
And AGM needs about another tenth per cell; so something around 13.8 for FLOAT......which means just maintaining the charge without adding much or any.

 

You insist on continuing to say that......and I think it is wrong.
Do you have some reference that leads you to believe that ??
I can't find anything that says the true resting voltage should be more than 12.9.

 

i would let it sit overnight disconnected, then check it.

reconnect, check it tomorrow night after it has been off an hour, then check it again sunday morning.

that should give you a pretty good idea where you're at.

 

Further to what bisco said and extending on that, that voltage looks good, leave it disconnected to sit overnight and confirm that it is still 13.x Volts. If it has dropped to (say) 12.4 V or less, you may have an issue. That issue may be just a bad battery, especially if you have dipped below 12.0 V overnight. If that is not the case, you can connect up the battery and retest the next day. If it has dropped to (say) 12.4 V or less, you may have an issue with parasitic draw.

At this point, you could put a multimeter (set to Amps – start at the highest and work down to lower scales) in series between negative post and ground, see what current (Amp) is currently being drawn. To do this successfully, you need to make sure all key fobs are more than 3 yards away from the car, have all doors shut and the ammeter connected in a way that you can see it from outside You then wait for 30 - 40 min to ensure the car has fully quiesced (i. e. all unnecessary systems have shut down). In this state, the draw should be ~20 mA, with very short periodic bursts to 40-50 mA.

If it is higher than this, you will then need to perform some testing for parasitic draw.

This is a good video that will give you the concept: How to Perform a Parasitic Draw Test | EricTheCarGuy

Good luck with your endeavors.

 

Almost. That 13.3 is not a "real" voltage but what is most often called "surface charge".
The voltage will drop rather quickly to the real resting value once a load is applied or it sits for 24 hours.

So.....you need to hook up the cable, which will activate some onboard systems and draw off the extra surface charge.
Take your "base" reading after about an hour.......and then let it sit overnight to see how much more it drops.

Note: It really is NOT necessary to disconnect anything to charge the battery in place.

 

Charging the battery is treating the symptom not determining the cause.

This. Please describe daily use.

 

Not necessarily true.
That usually should be the FIRST step in determining the cause.......of any electrical anomaly.