Schumacher 200.71230 Hydrometer or Electronic Method, Specific Gravity Percent of Charge Needed

13.2 The Hydrometer or Electronic Method

To find 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 specifica- tion sheet or the owner’s manual.

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 setting (2 or 10 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 of
Charger Setting			charge
100 (AH Rating) x .50 (charge needed) x	1.25	=	1.25
50 (Charger Setting)			hours

100 x .50 = 1 x 1.25 = 1.25

50

You will need to charge your 100-Ampere Hour Battery for approximately 1 1/4 hours at the 50-Amp charge rate using the above example.

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