1. How do I choose a battery charger?

The type of battery, the capacity of the battery and the time available for charging will determine the type and performance of the battery charger you need. An AUTOMATIC/SMART charger is your best choice for any kind of battery. Since damage to the battery could result if a MANUAL charger is forgotten to be disconnected from a fully charged battery allowing it be over-charged. A rule of thumb is to choose a battery charger capable of a charging current (in amps) 1/10th of the battery capacity in amp-hours. For example, a 50 amp-hour battery would require a charger capable of delivering 5 amps. It goes without saying that if you chose a 5 amp charger for a 100 Ah (amp-hour) battery, it would take twice as long to fully charge the bigger battery. A lower charge rate will do the battery no harm but a much higher rate may result in only a surface charging of the battery not allowing the chemical forming to take place as well as excessive gassing and progressive damage of the battery’s internal plates. Be aware that battery chargers sold throughout South Africa must be tested and certified by SABS. These tests are conducted against a compulsory specification. Any manufacturer or importer should make these test results available upon request to the customer. The best all rounder automatic battery charger in the Hawkins stable is the AutoPro 10 12/24V which incorporates a 5 amp and 10 amp selector switch.

2. How long does it take to charge a battery?

It follows from 1/10th rule that it will take about 12 hours to fully charge the battery because of roughly 10% heat and conversion losses. Batteries may be charged at higher rates but the manufacturers specification should be followed for maximum charge rate. This is a guide for a battery in good condition and there may be considerable variations either way depending on the battery condition or state of charge.

3. What is a taper charger?

It is a charger in which the charge current delivered to the battery decreases or tapers down as the battery gets fuller. As in the case of the Power 10, PRO 15 – 30, the battery is full when the charge current gets close to 0 amps indicating that no more current is flowing into the battery.

4. What is a trickle charger?

This is a common expression but there is no such thing as a charger expressly designed to “trickle”. The so-called trickle charger turns out to be nothing more than a small, usually cheap charger. Any uncontrolled charger will continue to deliver (or trickle) current into the battery as long as the battery voltage will allow it to do so. One of the potential dangers of trickle chargers are the false sense of security implied by the name. A continuous trickle current into a battery over time will take the battery into the gassing stage and if the battery is not monitored, it will lose water and suffer permanent damage. Except for automatic chargers, all other chargers have to be monitored to prevent overcharging.

5. What is the best charger for a battery that is not used often or for standby applications?

A small automatic charger, such as the Hawkins Smart 6, is the best charger for this purpose. Such a charger will sit quietly in the corner charging away and switch itself off when the battery has reached the set-point of the charger. Generally it will maintain the battery voltage for weeks, months or years if need be so that the battery is available at a moment’s notice. A powerful charger is not required as the battery is not used often and there is much time available. For this application, you can ignore the 1/10th of the battery capacity rule. If you are charging the battery whilst on the vehicle make sure the charger is capable of delivering enough current to charge the battery and cope with parasitic drain (e.g. alarm system, door locks etc).

6. What is an engine starter?

Chargers capable of starting a vehicle with a minimum of delay are generally labelled power boosters or engine starters. They work on the principle that the battery will safely accept a short high charge and then together with the charger, crank the engine. Specially designed circuitry is required to cope with the high currents encountered during engine cranking. The size of the vehicle and its battery will dictate the rating of the charger.

7. Can the battery be charged while still on the vehicle?

Yes, provided you observe all the safety instructions enclosed with the charger. The safest practice is to charge away from the vehicle. Please read the vehicle handbook to make sure that charging on the vehicle is permitted. Make sure the area in which you are charging is well ventilated. Charging the battery into its gassing stage will liberate explosive gases so remember no naked flames or sparks are permitted near the battery and be careful with metal tools. If you drop one it may cause a spark or short circuit the battery or other electrical component and cause an explosion. Follow this procedure.


If applicable, loosen and remove all screw caps over the cells (flooded type battery allowing water addition) Check that the plates are covered to a depth of approx. 10mm by adding distilled water where necessary. Do not overfill. Set any switches on the charger to the correct voltage and current selection. Connect the charger’s positive lead to the positive battery post. Connect the charger’s negative lead to the vehicle’s chassis/under-body remote from the battery and any fuel lines. Connect the battery charger to the mains outlet socket. Switch on at the mains and commence charging. If accessible, monitor the battery’s condition from time to time with a battery hydrometer and adjust any current control switches appropriately. Remember switches tend to produce arcs or sparks – another reason for being in a well-ventilated area. When the charge is complete (SG 1.24 –1.30) switch off at the mains, remove the plug from the mains socket and disconnect the charger in the reverse order to the above.


Connect the charger’s positive lead to the positive battery post. Connect the charger’s negative lead to the vehicle’s chassis/under-body remote from the battery and any fuel lines. Connect the battery charger to the mains outlet socket. Switch on at the mains and commence charging. Completion of charge will be indicated by the GREEN led illuminating, remove the plug from the mains socket and disconnect the charger in the reverse order to the above.

8. Why the concern about overcharging?

As the battery approaches its point of full charge, the chemistry of formation of lead oxide and lead on the positive and negative plates reaches completion. Any further rise in voltage across the cell at this point will result in an electrolytic decomposition and bubbles of oxygen and hydrogen will be evident. Some of the oxygen is used to make additional lead oxide and in doing so, some lead from the plate is permanently consumed. The result is a weakening of the positive plate that will eventually cause it to fall apart. The excess hydrogen and oxygen will leave the cell and the level of the battery water will drop. This should be topped up with distilled water. In the case of a sealed battery, gases that are unable to recombine will eventually be released through a one-way valve and when the plates get too dry, the battery will cease to operate. Bubbling is often seen long before a total full charge is reached and this is usually due to some points on the plate reaching a high voltage before the rest. High current flows and tight packing within the battery that prevents circulation of the acid aggravate this situation and this is the reason for moderate charging rates at the end point. In the case of sealed cells, reduced voltage ripple is used together with voltage regulation to minimise gas loss. Modern cars use sophisticated voltage control of the alternator for the same purpose. It is a very good idea to charge the car battery overnight every week or fortnight and an automatic charger makes the job simple. This regular charging, particularly if you do a lot of urban stop start driving, can add years to the life of the battery by preventing the slow accumulation of irreversible sulphate deposit on the battery plates.

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