Calculating charge time, Chart Method

Calculating charge time

The Chart Method

Use the following table to more accurately determine the time it will take to bring a battery to full charge. First, identify where your battery fits into the chart.

•Small batteries — motorcycles, garden tractors, etc.

— are usually rated in Ampere Hours (AH). For example; 6 to 12 AH, or 12 to 32 AH.

•Batteries in cars and smaller trucks are usually rated in Reserve Capacity (RC), Cold-Cranking Amps (CCA), or both.

•Marine, or deep-cycle batteries are usually rated in Reserve Capacity (RC).

•NR means that the charger setting is NOT RECOMMENED.

Find your battery’s rating on the chart below and note the charge time given for each charger setting.

The times given are for batteries with a 50-percent charge prior to recharging. Add more time for se- verely discharged batteries.

	BATTERY SIZE/RATING					CHARGE RATE/CHARGING TIME - HOURS
	BATTERY SIZE/RATING					2 AMP	10 AMP
						2 AMP	10 AMP
SMALL		Motorcycle, garden		6	- 12 AH	2 - 4	NR
BATTERIES		tractor, etc.		12	- 32 AH	4 - 10	NR
		200	- 315 CCA	40	- 60 RC	11 - 14	2 - 27/8
CAR/TRUCKS		315	- 550 CCA	60	- 85 RC	14 -18	27/8 - 33/4
		550	- 1000 CCA	85	-190 RC	18 - 35	33/4 - 7
MARINE/DEEP CYCLE				80 RC		18	31/2
MARINE/DEEP CYCLE				140 RC		27	51/2
				140 RC		27	51/2
				160 RC		30	6

				180 RC		33	7

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

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

Charger Settingof charge

100 (AH Rating) x .50 (charge needed) x 1.25 = 6.25

10 (Charger Setting)

hours

100 x .50 = 5 x 1.25 = 6.25

You would need to charge your 100-Ampere Hour Bat- tery for approximately 6¼ hours at the 10-Amp charge rate using the above example.

Sears 211 - Sch 510 9/14/95