Xantrex Technology 1200 - Manual (Page 65)

Battery Types and Sizes
B–8
Battery Connections Connections to battery posts must be made with
permanent connectors 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 Charge You can measure battery state of charge with
a hydrometer or 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
12.7–13.0 100%
12.5–12.6 80%
12.3–12.4 60%
12.1–12.2 40%
11.9–12.0 20%