Thought i'd give mine a recon charge ahead of the winter. Ran the agm recon mode on a ctek 5.0 charger but had to switch off after several hours whilst it was in recon mode (stage6). Used to get 14.5 volts reading but nows it 12.5 ish. Perhaps i should have finished the program. Should i give it another shot or have i ruined the battery? Or am i just stressing over nothing? Any thoughts guys?

 

Honestly guys, I think you are putting way more thought about this than is necessary.

Nominally a battery is usually about 12.5VDC when fully charged and not providing a load. And the charging system provides a higher voltage to it from the alternator/charging circuitry to keep it charged..

The voltage that is provided at the battery terminals can vary based on a number of factors including the instantaneous load and current battery charge level. For example the current voltage might be higher after starting up after the battery has been draining down for a while. There are all kinds of other loads present at different times when running that can cause the load on the battery to vary, and the voltage you see is reflective of the charging system attempting to keep the battery charged given several different factors. .

One thing to consider is that the charging circuitry knows how much "load" is being generated by monitoring the current flow. So under heavier load conditions (i.e. electrical consumption) it can provide a higher voltage to keep the battery charged.

What that voltage is at any given moment can vary so it wouldn't surprise me to see it anywhere from 12.5V to 15 VDC... so trying to guess and compare notes on why it is 13V at one instant and 15 at another is pretty much pointless..

The real concern is if the battery is not charging properly for some reason (i.e. bad battery cell or charging system failure) which most likely is going to be detected by the system.. Over voltage is a possibility as well, but that is a bit more rare and would likely be flagged as a fault by the system.

With a worn out battery you can see it since it doesn't hold a charge well and will have a tenancy to droop down voltage wise especially when the engine is off and under light load... Sometimes it is difficult to tell if it is the battery or the charging system, and in the old days you had to do a load test but a modern charging system can easily diagnose itself when something has gone wrong and should generate a fault.

My point is, staring at the volt meter and trying to compare instantaneous voltages is a bit misguided unless it is under specific known conditions.. In reality the current flow with an ammeter is much more valuable to tell what is actually going on than voltage.

In general unless I'm having problems I'm not going to spend anytime worrying about the instantaneous voltage displayed. Most likely if it was too high or too low you are going to get a fault displayed.

There is some value in looking at it just after shutting the engine down... (and not charging) and if I were to see it drooping down it is a hint that the battery is poor health or not being charged properly.

 

Not sure how you are measuring that voltage (i.e. 12.5 vs 14.5) and the conditions. (is the car running or off).. When running the battery voltage can vary widely depending on what the charging system is doing at any given instant.

A fully charged battery (when disconnected) should be around 12.5VDC... So if you are seeing 14.5VDC it would appear you are measuring it when the car is running.. A better check would be to do the comparison when the car is off and lightly electrically loaded.

Unless you are already having battery problems I think you are probably worrying about something that isn't a problem.

 

This wouldn't surprise me.. A battery is a chemical thing and tends to work and charge less efficiently at lower temperatures. I suspect the charging system in the 991 is fairly sophisticated and is going to respond with a slightly higher voltage to keep the battery charged.. (I don't know this for sure, but if I were designing the circuitry it would be an approach I would consider).

I also suspect the charging system is designed to counter aging of the battery and will respond in general with a slightly higher charging voltage to keep the battery charged. Again I don't know the details of the 991 design, but other battery charging circuits I've seen are capable of operating in that way which also can explain certain variations as well.

 

Thanks for the extensive and extremely useful replies scatkins. Certainly put my mind at rest. Just gonna keep on driving now :-)

 

Post the previous discussions, and as a follow up I did a little experimenting on my 991S...

With the engine off the voltage reads 12.5V, which is exactly what I'd expect for a good and fully charged battery.

When I started up, it was initially at about 13.5 VDC but over the course about a day I noticed it varied anywhere from about 13.3 to 14.6V... Tried different combinations of loading (headlights, rear window def, brakes applied etc..

In general, when switching on a load had at most a 0.1 V instantaneous impact. Rev'ing the engine a little (at idle) maybe a little more than that.

So bottom line... on this particular charging system it seems that the charging voltage varies all over the place. I suspect it is based on a combination of what the alternator is putting out and instantaneous loading. So it is hard to draw a conclusion of health simply based on reading the voltage when the engine is running..

I think a good periodic check of the battery itself would be to view the Voltage after driving (presumably the battery would be fully charged) and verify that the battery is at about 12.5V..

If it is less than that (12.5VDC) when the engine is off, but when running seems to be in the normal range (> 13.5V or thereabouts) range,,, most likely the charging system is doing it's job and may be that the battery is degraded (i.e. dead cell) or loosing it's ability to hold a charge.

If it seemed that the voltage output when running was always low (maybe just above the nominal 12.5 or low 13's and never climbed up to above 14V..(and never being after monitoring for a couple of days) Then I'd start suspecting the charging system might have an issue.