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• 13 •
The Hydrometer or Electronic Method13.2
To nd the time needed to fully charge your battery, determine the bat-
tery’s charge level with a hydrometer or electronic Percent-of-Charge
Tester. The following table will help you convert hydrometer readings to
percent of charge values.
SPECIFIC GRAVITY PERCENT OF CHARGE
PERCENT OF CHARGE
NEEDED
1.265 100% 0%
1.225 75% 25%
1.155 25% 75%
1.120 0% 100%
When you know the percent of charge and the Amp Hour (AH) rating of
your battery, you can calculate the approximate time needed to bring your
battery to a full charge.
To convert Reserve Capacity to Amp Hours, divide Reserve Capacity by
2, and add 16:
Amp Hours = Reserve Capacity + 16
2
NOTE: The Reserve Capacity can be obtained from the battery specica-
tion sheet or the owner’s manual.
To calculate time needed for a charge:
Find the percent charge needed. (A battery at 50 percent charge that will •
be charged to 100 percent needs another 50 percent (.50)).
Multiply the Amp Hour rating by the charge needed (.50) and divide by •
the charger setting (2, 15, or 60 amps).
Multiply the results by 1.25 and you will have the total time needed, in •
hours, to bring the battery to full charge.
Add one additional hour for a deep-cycle battery.•
Example:
Amp Hour Rating x charge needed x 1.25 = hours of
Charger Setting charge
100 (AH Rating) x .50 (charge needed) x 1.25 = 3.125
20 (Charger Setting) hours
100 x .50 2.5 x 1.25 = 3.125
20
You would need to charge your 100-Ampere Hour Battery for a little more
than 3 hours at the 20-Amp charge rate using the above example.