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.