Battery Charging Methods

Battery charging methods vary, based on several considerations: (1) electrical capacity of the battery being serviced; (2) temperature of electrolyte; (3) battery state of charge at start of charging period; and (4) the age and condition of the battery. When preparing to charge a battery, be aware of all the precautions that should be observed during the charging operation. Be familiar with the manufacturer's battery charger guide, and follow all the step-by-step instructions in the sequence given by the manufacturer. Ideally, use an automatic battery charger that senses battery voltage and automatically shuts off - or almost shuts off - when the battery reaches or approaches the fully charged state. These chargers include temperature sensing and generally sense polarity to help avoid sparks if the charger clamps are connected in reverse. Battery charging methods include "high rate fast charging", "constant potential charging", "constant current slow charging", and "trickle charging." "High rate fast charging" provides a high charging rate for a short time. Usually, the intent of a fast charge is to give the battery the "boost" it needs until the vehicle charging system can bring it to a full state of charge. The fast charging rate should be limited to 60 amperes for 12 volt batteries. Usually, the rate is set at 40 to 60 amperes for 30 minutes. To completely recharge a battery, the high rate fast charger should be adjusted to "slow charge," preferably at the rate of one ampere per positive plate per cell. For a battery with nine plates per cell, 4 (+) and 5 (-), the charging rate would be four amperes. "Constant Potential Charging," as the name implies, maintains the same voltage on the battery throughout the period of the charge. As a result, the current is automatically reduced as the battery approaches full charge. This features cuts the amount of overcharge the battery can receive, so batteries in good condition will not be damaged by this method of charging. If the battery is badly sulfated, the temperature may rise soon after it is placed on charge. These batteries should be placed on "slow charge." "Constant current charging" uses a low charging rate for a relatively long time. Charging rates of three to five amperes or one percent of cold cranking rating are typical, as is one ampere per positive plate per cell. Constant current slow charging periods as long as 24 hours may be needed to bring the battery to full charge. "Trickle charging" is designed to charge batteries at a rate of approximately one ampere. Trickle charges are used primarily for maintaining displays and stocks of batteries in fully charged condition. Common practice is to leave the batteries on a trickle charge during the day and take them off charge during the night. In that way, the danger of severe overcharging is lessened.