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Battery tips
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Discharged batteries Do not leave batteries in a discharged
state for more than a day or two. They will undergo a
chemical process (sulfation) that can permanently damage the
battery. As well, batteries self-discharge over a period of
three to six months, so they should be recharged periodically
even if they are not being used.
Electrolyte level If your batteries are not the “maintenance-
free” type, check the electrolyte level at least once a month.
Excessive fluid loss is a sign of overcharging. Replenish the
electrolyte using distilled water only.
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, more easily, with a voltmeter.
Use a digital voltmeter than can display tenths or hundredths
of a volt when measuring 10 to 30 volts. The batteries should
be tested with no load or charge source (batteries
disconnected) and should be open circuit for at least one hour.
The following table gives approximate state of charge for a
lead-acid deep-cycle battery at 77 ºF (25 ºC):
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%