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Calculating charge times
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 chad.
• 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 RECOM-
MENDED.
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. Add more time for totally discharged batter-
ies.
SMALL
BATTERIES
CAR/TRUCKS
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
60 - 85 RC
85 -190 RC
80 RC
140 RC
160 RC
180 RC
2-4
4-10
11 - 14
14 -18
18 - 35
18
27
30
33
NR
NR
V2-3A
_-1
1-2
NR
NR
NR
NR
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.
When you know the percent of charge and the Amp
Hour (AH) rating of your battery, you can calculate the
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 Caoacitv + 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).
• Multiplythe Amp Hour rating by the charge needed
(.50) and divide bythe charger setting (2 or 10
amps).
• Multiply the result by 1.25 and you'll have the time
needed, in hours, to bring the battery to full charge.
• Add one additional hour for a deep-cycle battery.
Example:
Amp Hour Ratlno x % of charo_eneeded x 1.25 = hours
Charger Setting d
charge
100 (AH Ratlno_ x .50 (charoQ needed) x 1.25 = 6.25
40 (Charger Setting) hours
- 1.25 x 1.25 = 1.5625
40
You would need to charge your 100-Ampere Hour
Battery for approximately 1½ hours at the 40-Amp
charge rate using the above example.
10