Battery charging tutorial-Part 2
18 Apr 2022


Equalization is essentially a controlled over charge. Some charger manufacturers call the peak voltage the charger attains at the end of the BULK mode (absorption voltage) an equalization voltage, but technically it's not. Higher capacity wet (flooded) batteries sometimes benefit from this procedure , particularly the physically tall batteries. The electrolyte in a wet battery can stratify over time, if not cycled occasionally. In equalization, the voltage is brought up above typical peak charging voltage (to 15 to 16 volts in a 12 volt system) well into the gassing stage, and held for a fixed (but limited) period. This stirs up the chemistry in the entire battery, "equalizing" the strength of the electrolyte, and knocking off any loose sulphation that may be on the battery plates.

The construction of AGM and Gel batteries all but eliminates any stratification, and most all manufacturers of this type do not recommend it (advising against it). Some manufacturers (notably Concorde) list a procedure, but voltage and time are critical to avoid battery damage .

Battery Testing

Battery testing can be done in several ways. The most popular includes measurement of specific gravity, and battery voltage. Specific gravity applies to wet cells with removable caps, giving access to the electrolyte. To measure specific gravity, buy a temperature compensating hydrometer at an auto parts store or tool supply. To measure voltage, use a digital voltmeter in the DC voltage setting. The surface charge must be removed from a freshly charged battery before testing. A 12 hour lapse after charging qualifies, or you may remove the surface charge with a load (20 amps for 3 plus minutes).

Load testing is another method of testing a battery. Load testing removes amps from a battery (similar to starting an engine). Some battery companies label their battery with the amp load for testing. This number is usually 1/2 of the CCA rating. For instance, a 500 CCA battery would load test at 250 amps for 15 seconds. A load test can only be performed if the battery is at or near a full charge. Some electronic load testers apply a 100 amp load for 10 seconds, and then display battery voltage. This number is compared to a chart on the tester, based on CCA rating to determine battery condition.

Sulphation of batteries starts when specific gravity falls below 1.225 or voltage measures less than 12.4 (12v Battery ) or 6.2 (6 volt battery). Sulphation can harden on the battery plates if left long enough, reducing and eventually destroying the ability of the battery to generate rated volts and amps. There are devices for removing hard sulphation , but the best practice is preventing formation by proper battery care and recharging after a discharge cycle. Sulphation is the main reason a significant portion of lead acid batteries doesn’t attain their chemical life span.

Charging Parallel Connected Batteries

Batteries connected in parallel (positive to positive, negative to negative) are seen by the charger as one large battery of the combined amp hour capacity of all the batteries. Thus, three 12 volt 100 amp hour (ah) batteries in parallel are seen as one 12 volt 300 ah battery. They can be charged with one positive and negative connection from one charger of the recommended amp output. They also can be charged with a multiple output charger, like a three bank unit in this case, with each battery getting its own connection at battery voltage. The charging amperage would be the sum of the individual output amps.

Charging Series Connected Batteries

Batteries connected in series are a different story. Three 12 volt 100 amp hour batteries connected in a series string (positive to negative, positive to negative, positive to negative) would make a 36 volt 100 ah battery pack. This can be charged across the pack with a 36 volt output charger of the appropriate amp output. They also can be charged with a multiple output charger, like a three bank unit in this case, with each battery getting its own connection at battery voltage (12 volts in this case) . Either method is fine, UNLESS one or more of the batteries are tapped at lower than system voltage. An example would be tapping one of the batteries in this 36 volt string at 12 volts for a radio or some lights, etc. This imbalances the pack, and charging at system voltage (36V) doesn't correct the imbalance. The multiple bank charger connecting to each battery is the correct way to deal with this series battery string, as it corrects the imbalance with every charge cycle.

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