Arduino Internal 1.1v ref

New to this.

Have looked at hundreds of postings, but not found answer.
Building battery capacity tester/charger station.
Was having problem getting accurate voltage readings.
Come to find out internal voltage references were off.
5.0 vdc = 4.69 vdc and 1.1 vdc = 1.08 vdc.
No problem since i use external DVM to get these new voltages.
Have 10 more Nanos, and most have different voltages.

What i am looking for is a way to get actual internal voltages to use in equations, with out having to test each and every board i use. (Would be a pain if had to replace board and forgot to test volt and change code for each board used)

Any ideas?

I think you looked at the wrong posts as it's been discussed here time and again. That internal reference is stable but has a tolerance of 10%, so you have to calibrate them one by one.

Alternative: use an external precision reference such as the TL431 and connect that to the Vref pin.

The internal 1.1V referance does have a stated tolerance of +/- 0.1V.

If thats not accurate enough for you then you need to use a more accurate external referance of choice.