Car Battery Charger

Overview of the car battery charger

Car batteries are “secondary” batteries, which means that, unlike “primary” or disposable batteries, they are rechargeable. Ordinarily they are kept fully charged by the normal operation of the car, with an alternator converting some of the power output of the engine into stored electrical energy. Unfortunately and often inconveniently, the charge capacity of a car battery will decay over time and it will reach a stage where the output is so low that it will fail to power the starter motor. If a vehicle’s lights are accidentally left on the charge will drain and will need to be replaced by using a battery charger. Sometimes an alternator develops a fault and will fail to pass enough electrical energy into the battery to keep it charged to a point where the electrical components on a vehicle can fully operate.

Unless the battery has deteriorated so badly that it can no longer hold a charge, a car battery charger is the most efficient way to recover a “flat” battery. Fast charging the battery using, for example, jump leads attached to another vehicle’s battery, or by subjecting the engine to high RPMs while the vehicle is stationary, may be unavoidable in an emergency but is actually an exceedingly harsh method that could reduce the lifespan of the alternator.

Car battery chargers are available in a range of shapes and sizes, with some being more easily portable than others. Many have the capacity to jump-start a partially drained battery but often they will not be able to do so with a completely drained battery. The more expensive chargers are usually equipped with additional features, such as a compressor for inflating tyres and a gauge for checking tyre pressures.

Heavy-duty car battery chargers are available, but their bulk and weight generally renders them unsuitable for carrying in a vehicle all the time, hence they are often kept in the garage at home. Smaller portable devices, although convenient, generally lack the power of the larger chargers.

If a car is to be kept in storage for any length on time, a small trickle charger will keep its battery optimally charged for extended periods. When doing this the charging process should be regularly monitored by keeping an eye on the device’s charge indicator lights.



The nineteenth century French physicist Gaston Planté is credited with inventing the first rechargeable

battery (and hence the first battery charger) in 1859, when he unveiled his lead-acid battery – the prototype of the present day car battery and car battery charger. His concept was eventually commercially utilised in the manufacture of motor vehicles. As cars became more affordable and ubiquitous the manufacture of standalone battery chargers became commercially viable and they were seen as an essential part of a car owner’s toolkit. In the early days a dynamo rather than the more efficient alternator was used to charge a car’s battery, as a result battery failure was far more common when it was subjected to heavy demand.


Technical aspects

Basically, car battery chargers use a transformer and a full wave or half wave rectifier to convert wall-outlet 220V alternating current into a 12V direct current that is then fed into the battery (the transformer reduces the voltage, while the rectifier converts AC to DC).

Of considerable importance from a health and safety angle is the potentially hazardous process of “gassing” during recharging, during which hydrogen gas is released from the sulphuric acid bathing the lead plate electrodes. This can build up and become explosive, especially during rapid charging. If the battery becomes overcharged the gassing can escalate, and should an internal spark occur, for example, the hydrogen will react with environmental oxygen to produce a highly flammable gas. For this reason, personal protective equipment, such as goggles, gloves and overalls is highly advisable when using a car battery charger. This applies particularly with the simpler models of charger that do not include an automatic charge current regulator. It is essential to monitor the charging process carefully at all times throughout the process.

More sophisticated chargers can charge the battery quickly, safely and completely without the need for manual intervention. Chargers such as “IUoU” models safely employ a three-phase (I-phase, Uo-phase and U-phase) process to rapidly charge car batteries, automatically stopping when the charging is complete.

One significant limitation of lead-acid car batteries is the tendency for a crystalline patina of lead sulphate to form on the surface of the lead plates. This is due to their electrochemical reaction with the sulphuric acid in which they are immersed. This “sulphation” tends to occur when the battery is discharged over an extended period and it always impedes recharging. However, if extended discharge is avoided, sulphation can be reversed during recharging, and specially designed desulphating car battery chargers are now available to minimise the presence of the lead sulphate crystals.


Current car battery benefits and limitations

Simple chargers are relatively inexpensive and conveniently portable but they require careful monitoring by the user: they must be disconnected before “overcharging” the battery because of the danger of potentially explosive “gassing” as described above. Automated car battery chargers are more expensive but avoid this danger; chargers capable of rapidly jump-starting a partially drained battery are useful but the more powerful models tend to be large and heavy, rendering them almost non-portable by domestic users.