Battery Basics

In Articles, Technical by Glyn DemmerLeave a Comment

Okay I have never pretended to be a rocket scientist so when recently faced with a flat battery I did the normal and took the battery home, charged it for a few hours and then refitted it and started my bakkie!

All good and well but why was the battery flat? Well quite simply I had parked and left my lights on for the duration of a pleasant Fathers Day lunch with the family. After this minor inconvenience I decided that I needed to know more about batteries and contacted an old friend Johan Mostert of Bridgestone Fundi fame who now runs a concept adventure store for Dixon Batteries a manufacturer based in Vereeniging. I wanted to see how a battery was made and ask a few questions and perhaps share the information with any other luddites out there!

To start a vehicle it must be able to draw sufficient current (energy) from the battery and operating of electrical devices with the engine off within reason should not hinder successive attempts to start the engine.Generaly these are covered by the abbreviation SLI – starter ,lights and ignition. Thus the battery, starter and the electrics should be designed to be totally compatible. The only deviation in this case would be the requirement to run aftermarket electrical equipment such as lighting systems and fridges, however we will cover this later when we look at dual battery systems and deep cycle batteries.

So lets look at a typical battery, it comprises a set of cells housed individually in a polypropylene case, each cell has positive and negative plates and the battery is filled with an electrolyte solution. The posts or terminals, cell connectors and the plate straps are all connected. The battery cover is bonded under temperature to the case and in the case of a conventional battery each cell is sealed with it’s own plug. Maintenance free batteries do not have these plugs but do have the so-called escape vents.

The maintenance free batteries fitted to most vehicles have no need to check the electrolyte; in fact there is normally no mechanism or way to do so! Other than the two breather vents this battery is completely sealed. So what next, what do we need to know to enable us to understand this often overlooked but critical piece of equipment.

Charging is crucial, when running in the vehicle this will be limited so that the charge current drops as the battery voltage increases, this is done to prevent overcharging and prolong battery life. Most home chargers do not have this ability and the charge rate should be monitored to avoid damaging the battery.

Obviously the discharge rate is critical  (especially when the engine is not running) as this leads to a flat battery per my example having left my lights on! Discharge is initially gradual however continued load leads to a complete discharge and the so-called “flat battery”.

Generally the battery specified by your manufacturer fitted to your vehicle will be adequate for daily use however conditions do place demands on batteries, starting in winter (especially if the vehicle is left out) draws higher current, even more so if the vehicle is Diesel powered). Frequent stop start driving does also affect the batteries ability to maintain a positive charging balance; this makes it important for the battery to deliver an initial high voltage for starting and still be able to furnish some of the energy required to run electrical components at low revs or when switched off.

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