[DavidU (Dave)]

Batterys are non regulated but at full charge give a very smooth 12V in this case.
A regulator like an LM 7812 is a 3 legged TO220 device (looks like a drive transistor) will "regulate" any higher voltage (within certain current draw perameters) to, in this case 12V up to the devices current limitations (in the case of the LM 7812) 1.2A.
So, feed a 12V regulator 14v it gives 12. Give it 16v it will deliver 12V (up to 1.2A) in this example.Give it 10V it aint going to give 12v.
So a battery starter pack is not going to have a 40A regulator.
Most modern astro steppers/ cameras/ drives etc are as I see are designed for FULLY regulated DC supplys. Once a fed device is BELOW it's rated voltage you will get all sorts of faults/anomalies.
However ! Some astro devices have there own regulators.
Please read the little spec sheet that comes with your expensive equipment, it may say..... 12-14V DC 500MA ( this device may well have an internal regulator)
If it says.... 12V fully regulated supply needed. well that says it all.
I have seen thousands and thousands of $ damage by end users not using the correct power supply's.