Someone else might be able to correct me, but a car battery while billed out as 12V is usually more like 13v+
Seems high risk to connect to your board. Just my $.02
That's only when charging. Nominal voltage on SLA cells is between 2 and 2.15 volts fully charged. Generally I read around 12.2 on a battery that's been sitting for a few hours. My instructions say to always test voltage first and don't do it while the car is running because then you are correct. Charging voltage is usually around 13.5.
Carman - I have a microscope, going to go over that board I connected to the battery in the next day or so, have been occupied. Will also measure voltage on battery,
car WAS off at the time. I'm sure its close to 12V tho, so will gather that info just for the record.