The absorption mode applies a peak charge of 14.4-14.7 volts until the battery is fully charged. The charge current then tapers, and voltage is kept constant at a set level. The final pulse mode sends out current pulses, and charging ranges from 95 to 100 percent. The battery receives a pulse if its voltage falls. This stage keeps a battery in good condition although it's not being used on a regular basis. The compact CTEK charger is fully sealed and weighs just over one pound.
National Parts Depot also offers the Deltran Battery Tender, primarily a maintenance-type charger. Its 1.25-amp constant-current reaches and maintains a full charge indefinitely by automatically switching to a storage charge. It won't overheat or overcharge a battery and it adjusts for temperature. In addition, the
Battery Tender has microchip circuitry that avoids shorting or sparking if the clips inadvertently touch each other. For example, if storing a car for the winter, NPD suggests removing the battery from the car and leaving the Battery Tender connected while the battery isn't in use. NPD also has a Battery Tender Jr., a more compact unit with a 750-milliamp current rating. It will also charge and maintain a battery.
A general-purpose charger, the sort sold at any auto parts store, is also worth considering and is usually available at a budget price. A good example is the Schumacher SE-82-6 dual-rate charger that we purchased at a local Southern California Kragen Auto Parts store for 25 bucks. The difference between a typical charger such as the Schumacher and the others mentioned is its higher amperage output. At its 6-amp charge rate, it'll charge a battery in about 6-8 hours. And while its 2-amp slow-rate setting is good for smaller batteries, this is a manual charger that will continue to charge even after the battery is fully charged. A visual check of the ammeter is required to know when the battery is fully charged. This unit is not as suitable for long-term low-amperage trickle charging on a stored battery.