If you’re having battery voltage-dependent issues with your cars electronics while the car is running then you need to consider the health of the cars charging system and grounding points.

A fully discharged car battery can't be fully charged any more because of the sulphation and the lifespan is shortened. You should not discharge it fully. Only a deep cycle battery is OK to discharge almost fully. Unfortunately car batteries are not designed so. The battery company Yuasa's home page says, "To ensure the batteries are not allowed to discharge to the point where they are damaged (sulphated) or so incapable of giving designed service life".
https://www.yuasa.co.uk/info/technic...ult-diagnosis/

Due to the sulphation occured, your battery's internal resistance is increased and the CCA is less than before. You can't expect a lot to your semi damaged battery. A good desulphator/regenerator can reduce the sulphasion some though.

I have driven my car running only on the battery (dead alternator) until it was completely dead and car would shut off, until I finally changed the alt. I would just throw in another charged battery and be on my way, until it died again. (never a 100% charged battery) Drove like that for a couple weeks, maybe 800 miles. Actually made a 300 mile trip (out of state) and had to stop at Autozone on the way back to get one of the batteries charged so I could make it back home. I never had any problems with any other electronics during that time, or afterwards.
I would think, if your battery was below 25% and driving it "would not charge it to 100%", then your alternator was bad and that might be causing whatever electronic problems you have until you change that.

My car can sit a week,2 or even more. I got a battery tender and put a plug on the front bumper.Every time I drive car I plug the tender back in.Battery should last a long time. Plus training for when electric cars are all we are allowed to drive,plugging it in really takes no time or effort.

I do not like buying batteries.

I checked my two LS400 . Was sitting idle at ca 12.7 to 12.8 V almost full.
I have a volt meter attached when I drive.
It seems the charging system goes up a bit with the voltgage and then goes down a bit when it is considered full.
In summer it seem to be done topping up very fast.
The weak battery I had before threw warning messages CHECK WSC or simmilar which seems not unusual.
I think voltage went really low when starting.

You should be seeing driving 13.2v

13.8,or even 14.2v right after starting.Mine is never 12.7-8 unless I turn on everything running at idle.Odd you have 2 that are. How often do you drive it?

Im full in its your alternator,you shouldnt eat batteries unless its sitting.FWIW,hopefully others will chime in on their voltages.

I was unclear. Sorry .
Battery Idle => not in any use.
Hence ignition off and no loads at all for a minimum 3 hours or so.
Voltage then indicates well the charge level for a lead acid battery.
There are tables to find on this. Just Google "lead acid charge level"

For instance 12.60 V unloaded after a few hours means 75 % state of charge (at room temperature)
For a AGM (Acid Glass Mat) Lead acid battery .

Dear Forum Members, I have found an interim solution to my problem of a draining battery, that has plagued me since July of 2023. I left my car with an Auto Electric shop with multitudes of diagnostic equipment for several days and they could not find the problem.

I went online and bought a Battery Isolator for $4, which disconnects the battery from the electrical system, when the car is parked. You only have to turn a **** on the device, installed on your battery, to disconnect.

I have used it for 2 weeks, with NO DEAD BATTERY. Eventually, when whatever is causing the problem fails, I will get it fixed. JC