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Sears 201- Sch 506 1/9/98
Calculating charge timeCalculating charge time
Calculating charge timeCalculating charge time
Calculating charge time
The Hydrometer or Electronic MethodThe Hydrometer or Electronic Method
The Hydrometer or Electronic MethodThe Hydrometer or Electronic Method
The Hydrometer or Electronic Method
To find the time needed to fully charge your battery,
determine the battery’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 PERCENT PERCENT OF
GRAVITY OF CHARGE 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
To calculate time needed for a charge:
• Find the percent of 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 rate
(1.5 amps).
• Multiply the result by 1.25 and you’ll have the
approximate 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
Charger Setting of
charge
20 (AH Rating) x .50 (charge needed) x 1.25 = 8.33
1.5 (Charger Setting) hours
20 x .5 = 6.66 x 1.25 = 8.33
1.5
You would need to charge your 20-Ampere Hour Bat-
tery for approximately 8 hours at the 1.5-Amp charge
rate using the above example.