It is common for modern electronic equipment rated at a nominal voltage of 12VDC to be able to accept a voltage range as low as 10V. (The minimum operating voltage can usually be found printed on the equipment or in the manual.)

However, some equipment will cease to operate at voltages lower than your battery is putting out. For instance, the Fostex PD-4 will not operate reliably when the external voltage drops below 11VDC, even though your battery supply may still have plenty of useful current remaining and your other equipment continues to operate. Another example are the Cooper 106 and 108 mixers that need at least 15 volts for full spec. The 15 Volt juicer will always output 15 volts even when the supply voltage is as low as 10 volts.