Voltage Regulator??

You can buy a cigarette-lighter voltmeter, which I use in my newer vehicles on trips so no surprises. The Harbor Freight one has LED lights, that show 14 - 14.5 V as "normal" when driving, as I recall, and a digital Equuis one I have suggested similar, I recall, so must be the setpoint of most Vreg's. I can't comment on Redfish statement that batteries have changed, other than I thought lead-acid battery technology hasn't changed in 100 yrs, other than making them cheaper and less reliable today w/ thinner lead plates that sulfate easier, plus prices seemed to have gone up much faster than inflation. Regardless, if you do apply too much voltage you will start dissociating the water into H2 & O2, i.e. "hydrolosysis", but probably requires >15 V.