Schumacher MSC-2405 User Manual

Page 11

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CALCULATING CHARGE TIME

14.

To determine the time needed to fully charge your battery, you must

first determine the battery’s charge level with a hydrometer or electronic

Percent-of-Charge Tester. The following table will help you convert hy-

drometer readings to percent of charge values.

Specific Gravity

Percent of Charge

Needed

1.265

100%

1.225

75%

25%

1.155

25%

75%

1.120

100%

When the percent of charge and the Amp Hour (AH) rating of your battery

is known, 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:
Example:
Amp Hour Rating = Reserve Capacity + 16

2
NOTE: The Reserve Capacity can be obtained from the battery specifica-

tion sheet or the owner’s manual.
To calculate the 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 (.5)).
Multiply the Amp Hour Rating by the charge needed (.5) and divide by

the charger setting (5 amps).
Multiply the results by 1.25 and you will have the total time needed, in

hours, to bring the battery to a full charge.
Add an additional hour for a deep-cycle battery.

Example:
Amp Hour Rating x % of charge needed x 1.25 = hours of charge

Charger Setting
100 (AH Rating) x .50 (charge needed) x 1.25 = 12.5 hours

5 (Charger Setting)
100 x .50 x 1.25 = 12.5

5
A 100-Ampere Hour Battery must charge for 12 ½ hours when using the

above example.