Schumacher 00-99-000207 - Manual (Page 13)

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0.4 The temperature of the battery and the equipment the battery is used with has a dramatic effect
on battery efficiency and system power requirements. For example, at 0 o F (–8 o C), a battery
is operating at 40% of its rated efficiency, while the engine it is attempting to start requires over
twice as much power as would be necessary at 80 o F (27 o F).
11. BATTERY CHARGING
. Determine battery’s state of charge by following the instructions and chart in Section 0, connect
charger as per instructions in Section 7 and/or 8.
.2 From the Charging Time Chart (located in the Quick Reference Guide Section), pick the ROW
which has the Reserve Capacity rating and measured battery voltage that is closest to the battery
being charged. Follow across the row until you are under the desired charging rate. This value
indicates the approximate time required to recharge the battery.
.3 An alternative method for calculating the time required to recharge a battery in good condition is
to follow this formula:
(reserve capacity in minutes) + 15.5 = amp hour capacity
2
(amp hour capacity) x (percent of charge needed) = time in hours
charger amp rate setting
(time in hours) x (recharge factor of 1.25) = recharge time
Example: Suppose a battery has an RC of 20 minutes and is discharged down to 25%. We need
to put in 75% more charge and we want to use our charger’s 40 AMP charge setting:
120 minutes + 15.5 = 75.5 amp hours
2
(75.5 amp hours) x (0.75) = time = 1.4 hours
40-amp charge rate
Then: (1.4 hours) x (recharge factor of 1.25) = 1.76 hours or 106 minutes recharge time.
12. MULTIPLE BATTERY CHARGING
2. PARALLEL CHARGING
Batteries of the same type and voltage rating may be connected in parallel for maintenance
charging. Charge time increases in proportion to the number of batteries. Rate of charge decreas-
es in the same proportion.
Example: Charging 2 batteries in parallel will take 2 times longer; each battery receives /2
the amount of charge showing on the ammeter. Thus, if the ammeter shows a 40-amp charge,
each battery will be getting a 20-amp charge (when batteries have the same rating, same
state of charge, etc.).