Schumacher 85-8100 instruction manual Battery Charging Formula

**Initial specific gravity readings vary, depending on battery type and manufacturer. Contact the seller or manufacturer of the battery for this specification.

11.2The state-of-charge of sealed-top (maintenance-free and recombination-type) batteries must be checked with a high resolution voltage tester.

11.3If uncertain about type of battery you will be charging, or the correct procedure for checking the battery’s state-of-charge, contact the seller or manufacturer of the battery.

11.4The 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 oF (–18 oC), 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 oF).

12. BATTERY CHARGING FORMULA

12.1Determine battery’s state-of-charge by following the instructions and chart in Section 11, connect charger as per instructions in Section 9 and/or 10.

12.2From the Charging Time Chart (located on the Table of Contents page and also on the Quick Reference Guide), 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.

NOTE: As a manual charger, the NAPA 85-8100will continue to charge for as long as the Timer is selected. This is potentially dangerous, as battery thermal runaway and gassing are not detected. For this reason, only set the Timer for slightly over the needed time to perform a charge. More time can always be added later, as the Timer keeps track of accumulated time and charge.

12.3An 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 120 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:

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