As far as I am aware, Most stuff can normally run below 12v, Its when you get below 9 that you start having issues.. You can have a battery that reads 12v but the acid can still be pretty gay, Volt meter is not the best way to test a battery's condition, Hydrometer will tell you how well the battery is charged. To test it properly in theory you have to take the surface charge off the battery by loading it up to half the CCA rating of the battery for like 20 seconds and check it doesn't fall below 9V..