Battery Chargers

Today most high quality battery chargers rely on microprocessors to charge batteries; using a 3 stage charger will help prolong battery life and your return on investment. Lower quality chargers may only have 2 stages and may not fully recharge your battery, causing sulphation and shorter life span. Three stage chargers are referred to as “intuitive chargers” and are recommended for maximum return on investment. The three stages of charging are bulk, absorption and float; equalization is sometimes considered another stage. It is important to use battery manufacturer’s recommendations on charging procedures and voltages to maintain battery capacity and service life.

“Intuitive chargers” are designed with the latest charging philosophy in mind and also monitors information from the battery to provide maximum charge benefit with minimum observation. Pro Charging Systems units are preferred for their suitability and performance for all types of batteries. Gel cell and AGM batteries may require special settings or chargers (refer to manufactures specs). Peak charging voltage for Gel batteries is 14.1 or 14.4 volts, which is lower than a wet or AGM type battery needs for a full charge. Exceeding this voltage in a Gel battery can cause premature failure and/or shorter life span.

Most battery manufacturers recommend sizing the charger at about 20% of the battery capacity. There for an 80 ah (ah = amp hour capacity) battery would take about a 15 amp charger (or less). Larger chargers may be used to decrease charge time, but may cause over charging and decrease battery life. Smaller chargers (1 or 2 amp) are fine for long term floating, but will not charge a deeply discharged battery.

Three Stage Battery Charging

BULK stage involves about 80% of the recharge, wherein the charger current is held constant (this is referred to as a constant current charger), and voltage increases. The properly sized charger will give the battery as much current as it will accept up to charger capacity, and not raise a wet battery over 125° F, or an AGM or GEL (valve regulated) battery over 100° F.

ABSORPTION stage (the remaining 20%) has the charger holding the voltage at the charger’s absorption voltage (between 14.1 VDC and 14.8 VDC, depending on charger manufactures set points) and decreasing the current until the battery is fully charged. Some charger manufacturers call this absorption stage an equalization stage. If the battery won’t “hold” a charge or the current does not drop after the expected recharge time, the battery may have some permanent issues. Please have the battery inspected by a professional.

FLOAT stage is where the charge voltage is reduced to between 13.0 VDC and 13.8 VDC and held constant, while the current is reduced to less than 1% of battery capacity. This mode can be used to maintain a fully charged battery indefinitely, without damaging the battery.


Equalization Stage

Many charger manufacturers call the peak voltage the charger attains at the end of the BULK mode an equalization stage or charge, an equalization charge is a controlled over charge. Some wet (flooded) batteries sometimes benefit from this procedure, particularly physically larger batteries and/or higher capacity batteries. The electrolyte in a flooded battery can stratify (layers of electrolyte separate from water) over time, if the battery is not cycled occasionally. In equalization, the voltage is brought up above typical peak charging voltage (15 to 16 volts in a 12 volt battery) well into the gassing stage and held for a fixed (but limited) period. This stirs up (boils) the electrolyte in the battery, “equalizing” the strength of the electrolyte and helps in removing any loose sulphation that may be on the battery plates. The construction of AGM and Gel batteries all but eliminates any stratification, and most manufacturers of AGM/Gel batteries do not recommend equalization for their products.

Charging Parallel Connected Batteries

Batteries connected in parallel (positive to positive to positive to positive, negative to negative to negative to negative) are seen by the charger as one large battery of the combined amp hour capacity. Thus, four 12 volt 100 amp hour (aH) batteries in parallel are seen as one 12 volt 400 ah battery. The battery pack can be charged with one positive and negative connection from one charger. The battery pack also can be charged with a multiple output charger, like a four bank unit in this case with each battery getting its own connection. The charging amperage would be the sum of the individual output amps.


Charging Series Connected Batteries

Batteries connected in series are a different than parallel. Four 12 volt 100 amp hour batteries connected in a series string (positive to negative, positive to negative, positive to negative, positive to negative) would make a 48 volt 100 ah battery pack. This battery pack can be charged with a 48 volt output charger of the appropriate amp output. This battery pack also can be charged with a multiple output chargers (like a four bank unit) with each battery getting its own connection at battery voltage (12 volts). Both methods are fine, UNLESS one or more of the batteries is tapped at lower voltage system (lights, radio…). This imbalance in state of charge in the battery pack and charging with a single 48 volt charging system will not correct the state of charge imbalance. The multiple bank chargers connecting to each battery is the proper way to address the imbalance, as it will correct the imbalance with every charge cycle.

Preparing to charge your car battery

It may be necessary to remove the automotive battery from the vehicle to charge it, always remove the grounded terminal first. Make sure all of the accessories in the vehicle are off, to prevent arcing and possible damage to vehicle. Be sure the area around to automotive battery is well ventilated while the battery is being charged. Clean the automotive battery’s terminals before charging. During cleaning, keep airborne corrosion from coming into contact with your eyes, nose, skin and mouth. You may consider using baking soda and water to neutralize battery acid and help eliminate airborne corrosion. Do not touch your eyes, nose and mouth. If required add distilled water to each cell until the battery acid reaches the level specified by the battery manufacturer, do not overfill the battery. For a battery without removable cell caps, such as valve regulated or sealed lead-acid-batteries, carefully follow the manufacturer’s recharging instructions (DO NOT REMOVE CAPS).

Read, understand and follow all instructions for the charger, battery, vehicle and any equipment used near the battery and charger. Study all of the battery manufacturer’s specific precautions while charging and recommended rates of charge. Determine the voltage of the battery by referring to the vehicle owner’s manual and make sure that the output voltage selector switch is set to the correct voltage. If the charger has an adjustable charge rate, charge the battery in the lowest rate first.

Charger location

Locate the charger as far away from the battery as the DC cables permit. Never place the charger directly above the battery being charged; gases from the battery will corrode and damage the charger. Do not set the battery on top of the charger. Never allow battery acid to drip onto the charger when reading the electrolyte specific gravity or filling the battery. Do not operate the charger in a closed-in area or restrict the ventilation in any way.

DC connection precautions

Connect and disconnect the DC output clips only after all of the charger switches to the “off” position and removing the AC plug from the electrical outlet first. Never allow the clips to touch each other.

A spark near the battery may cause a battery explosion.  To reduce the risk of a spark near the battery:

Position the AC and DC cables to reduce the risk of damage by the hood, door and moving or hot engine parts. Stay clear of fan blades, belts, pulleys and other parts that can cause injury. Check the polarity of the battery posts. The POSITIVE (POS, P, +) battery post usually has a larger diameter than the NEGATIVE (NEG, N, -) post. Determine which post of the battery is grounded (connected) to the chassis. If the negative post is grounded to the chassis (as in most vehicles), skip to the next step*. If the positive post is grounded to the chassis, skip to the step after next**. For a negative-grounded vehicle, connect the POSITIVE (RED) clip from the battery charger to the POSITIVE (POS, P,+) ungrounded post of the battery. Connect the NEGATIVE (BLACK) clip to the vehicle chassis or engine block, away form the battery. Do not connect the clip to the carburetor, fuel lines or sheet-metal body parts. Connect to a heavy gauge metal part of the frame or engine block. **For a positive-grounded vehicle, connect the NEGATIVE (BLCK) clip from the battery charger to the NEGATIVE (NEG,N, -) ungrounded post of the battery. Connect the POSITIVE (RED) clip to the vehicle chassis or engine block, away form the battery. Do not connect the clip to the carburetor, fuel lines or sheet-metal body parts. Connect to a heavy gauge metal part of the frame or engine block. When disconnecting the charger, turn all switches to “off,” disconnect the AC cord, remove the clip from the vehicle chassis and then remove the clip from the battery terminal. See Calculating Charge Time for length of change information on our Determining charge time page.


A spark near the battery may cause a battery explosion. To reduce the risk of a spark near the battery:

Check the polarity of the battery posts. The POSITIVE (POS, P, +) battery post usually has a larger diameter than the NEGATIVE (NEG, N, -) post. Attach at least a 24-inch long 6-gauge (AWG) insulated battery cable to the NEGATIVE (NEG, N, -) post. Connect the POSITIVE (RED) charger clip to the POSITIVE (POS, P, +) post of the battery. Position yourself and the free end of the cable you previously attached to the NEGATIVE (NEG, N, -) battery post as far away from the battery as possible – then connect the NEGATIVE (BLACK) charge clip to the end of the cable. Do not face the battery when making the final connection. When disconnecting the charger, always do so in the reverse order of the connecting procedure and break the first connection while as far away from the battery as practical. A marine (boat) battery must be removed and charged on shore. To charge it onboard requires equipment specifically designed for marine use.

Battery charging – AC connections

The battery charger is for use on a nominal 120-volt circuit (always refer to owners manual).

DANGER – Never alter AC cord or plug provided. If it does not fit the outlet, have a proper outlet installed by a qualified electrician. Improper connection can result in a risk of an electric shock.
Always use the recommended size extension cords for battery charger.


Batteries by Fisher recommended Pro Charging Systems units for all of your needs. Pro Charging Systems (PCS) builds high quality, leading-edge battery chargers designed to provide clients with value over the long-term. In short, PCS charging systems are designed and built to last. The company’s advanced DeltaVolt® technology enables their products to substantially out perform the competition. PCS provide significant additional value since their products charge batteries faster, maintain the charge for greater duration and make batteries last longer. That translates to greater productivity in industrial settings, happier boaters on the water, more time on the golf course and fewer batteries that have to be replaced overtime. The “value” multiplier for PCS products in most applications is significant. PCS line of chargers including the Professional, Sportsman, Eagle, Patriot and Recreation Series provide impressive performance designed to keep your equipment running longer between charges while extending the service life of your batteries. That is why Pro Charging Systems is the charger of choice for industrial lift equipment companies, boat manufacturers, golf cart owners, floor scrubber companies and other industrial users. It is also why many battery manufacturers endorse Pro Charging System chargers since they extend both the performance and the life of batteries. Please contact our customer service representatives today to discuss which Pro Charging System unit is best suited for your application.

You should always wear personal protection when charging and/or handling all batteries. The data and information contained herein are intended for use by persons possessing proper technical skill and knowledge, as they may deem appropriate and at their own risk. We assume no liability whatsoever for results obtained or loss or damage incurred as a result of application of any data or information presented herein. Batteries by Fisher, Inc. believes the information contained herein is accurate as of its publication date. Information contained herein is subject to change without notice.


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