After a charger is disconnected or the engine shut down, you MUST wait at least six hours to get a correct 'resting' voltage. Minimum 12.6 volts. No caveats, no 'close enough'.

 

I prefer to check the battery with it disconnected from the car as the car systems can cause spurious readings. When fully charged and still on the charger it should read around 14V. Then leave it disconnected overnight and test it the next day. It should be a minimum of 12.6V or 12.7V but ideally something even closer to 13V. Even this is not a definitive test as the battery might be delivering a decent voltage but be unable to deliver a decent current although if it turns over and starts well then that suggests that the current is fine. A good garage can do a better test with their more specialised equipment.

Richard

 

Tiepolo said the CTEK was in stage 7, at which point it should be supplying the battery 13.6v. 13.46v with the lights on is probably about right.

 

As said above you can’t get a usable battery voltage reading with the battery connected to the car. With the battery disconnected and fully charged I agree it should be closer to 13V as this’s been my experience as well. With the battery fitted and the generator off, you’ll see all sorts of voltages at 12V and higher which don’t necessarily mean the battery’s bad which why testers load test a battery to determine its true voltage and capacity. A simple DIY test with a VOM connected directly to the terminals then try starting the car. If the voltage stays above 10V it’s good, if it drops below 10V something’s off.

If the new battery starts fully charged and the vehicle sits for a week or more locked and you find the battery below 12V, then either the battery’s bad or there’s definitely something in the car’s electrics not shutting down.

 

FYI @Tiepolo For an AGM battery:
https://www.batteryskills.com/agm-ba...voltage-chart/

Lead-acid have a maximum charge of 12.6v.

As we have all pointed out, a battery at 12.4v is only at 50% capacity. And that is not the good.

 

There is what's known as a "surface charge" after charging a battery - from t'internet:

A battery with surface charge has a slightly elevated voltage and gives a false voltage-based SoC reading. To normalize the condition, switch on electrical loads to remove about 1 percent of the battery’s capacity or allow the battery to rest for a few hours. Turning on the headlights for a few minutes will do this.

So if yer trunk lights were on this would basically kill the surface charge - so 12.86 would be good. You could wait 5-10 mins with the trunk open and see what it is then.

 

Yep, different Ctek models, different batteries and different temperatures will, on average, produce something around 14V so 13.6V covers it in this particular case.

Richard

 

13.6v "covers it" because that's exactly what it is designed to output in stage 7.

 

I guess that I really don't know that much about batteries and the charging of them. Luckily my Bro was on hand to make all my earlier posts. 😉

Richard