Using a DMM, as long as it does go above 16v or below 12.5 you should be good.
Apparently u didnt see my second post haha but its ok i said i did check with dmm and it was the samestinger volt meters need to be set first off when u get them if u didn't with a DMM then its not reading right in the first place so i would use a dmm to set it and check your voltage take front cover off and there is a set screw inside on the board it shows u how in the paper work
x2colder it is, the higher the voltage sits. The hotter, the lower.