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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, identity 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 69-percent
charge prior to recharging. Add more time for severely
discharged batteries.
SMALL
BATTERIES
CARFRUCKS
BA'I-rERY SIZE/RATING
Motorcycle, garden
tractor, etc.
200 - 315 CCA
315 - 550 CCA
550 - 1000 CCA
MARINE/DEEP CYCLE
6 -12 AH
12 -32 AH
40 - 60 RC
6O - 85 RC
85 -190 RC
80 RC
140 RC
160 RC
180 RC
CHARGE RATE/CHARGING TIME - HOURS
2 AMP
2-4
4-10
11-14
14 -18
18 - 35
18
27
30
33
10AMP
NR
NR
2 - 27/8
27/8-33/4
33/4- 7
31/2
51/2
6
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 PERCENTOF
GRAVITY OF CHARGE CHARGE NEEDED
i
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 by2, 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 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 Setting of
charge
100 (AH Ratinq) x .50 (cherqe needed) x 1.25 = 6.25
10 (Charger Setting) hours
100x.50=5x1.25=6.25
10
You would need to charge your lO0-Ampere Hour Bat-
tery for approximately 61/4hours at the lO-Amp charge
rate using the above example.