Xantrex Technology XM 1000, XM 1800 manual Following table

Battery Types

Battery	Connections to battery posts must be made with permanent connectors
Connections	that provide a reliable, low-resistance connection. Do not use alligator
	clips. Clean the connections regularly and prevent corrosion by using a
	protective spray coating or Vaseline.
Battery State of	You can measure battery state of charge with a hydrometer or
Charge	approximate state of charge with a voltmeter. Use a digital voltmeter that
	can display tenths or hundredths of a volt when measuring 10 to 30 volts.
	Make your measurements when the battery has not been charged or
	discharged for several hours. For a deep-cycle battery at 77º F (25º C), use
	the following table:
	Battery Voltage	State of Charge
	12.7–13.0 V	100%
	12.5–12.6 V	80%
	12.3–12.4 V	60%
	12.1–12.2 V	40%
	11.9–12.0 V	20%

B–8 975-0263-01-01