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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 chosen.

    If it is a SEALED battery then an AUTOMATIC charger MUST be used. Serious damage to the battery could result if a MANUAL charger is used and has been forgotten on charge. If it is a flooded battery (with caps that allow the addition of distilled water) then either an automatic or a manually controlled charger will do.

    A rule of thumb is to choose a battery charger capable of a charging current (in amps) 1/10 th of the battery capacity measured in amp-hours. For example, a 50amp-hour battery would require a charger capable of delivering 5 amps.

    A lower charge rate will do the battery no harm but a higher rate and a manual charger, particularly at the completion of the charge, will lead to excessive gassing and progressive damage of the battery's internal plates.

    Be aware that many battery chargers displays numbers on the face that bear no relationship to the performance of the charger. All battery chargers retailed throughout SA 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.

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

    It follows from above that if you've chosen a charger using the 1/10 th capacity rule, it will take about 12 hours because of heat and conversion losses. 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 as the battery gets fuller. As in the PRO 15, the battery is full when the charge current gets close to 0.

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 (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 vehicle that is not used very often or for standby applications?

    A small automatic charger, such as the Hawkins SMART6, 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 time available. For this application, you can ignore the 1/10 th of the battery capacity rule but 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. electric alarm system, door locks etc).

6. What is an engine starter?

    Chargers capable of starting a vehicle with a minimum of delay are generally labeled 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.

    NOTE: The Hawkins range of Engine Starters MUST be plugged into mains and allowed to charge the battery for 10-15 minutes before jump starting a vehicle.

7. What can you use to check if a battery is good or bad?

    The Hawkins BLT600A is used to test a battery's ability to crank an engine. The BLT600A is capable of loading the battery under test to a maximum of 600A. The battery under test should be loaded to 3 times its amp hour (Ah) rating for 15 seconds. If the battery voltage falls into the RED zone (below 9V) during the test, the battery is regarded as being faulty and should be replaced.

8. 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 smoking or naked flames 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 /underbody 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 /underbody 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.

9. 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 in flooded batteries. This should be topped up with distilled water. In the case of a sealed cell or recombination 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 sulphation on the battery plates.

Manufacturers of a range of battery chargers since 1961 | sales@hawkins.co.za

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