Types of battery

  • Flooded – These batteries have a conventional liquid electrolyte (Lead acid). Standard types have removable caps so that de-ionised water can be added. Standard flooded batteries are cheap and if they are kept topped up they are not overly sensitive to high charging voltages. Sealed batteries have fixed valves to allow gases to vent during use.
  • Gelled Electrolyte – The electrolyte is a jelly and so will not leak. The electrolyte cannot be diluted such that over-charging must be avoided. These batteries may only last for 2 or 3 years in hot climates, although with good care they can last for 5 years.
  • Absorbed Glass Mat (AGM) Batteries – The electrolyte is held between the plates absorbed in a fine boron-silicate mat. Like gelled electrolyte batteries they will not leak acid but they can withstand more careless treatment and are less sensitive to over charging since they are designed to retain vented gases. AGM batteries can also stand for 30 days in a totally discharged state and still be recharged successfully. The major drawback to these batteries is that they cost between 2 or 3 times as much as flooded batteries.

Battery care

At least annually thoroughly clean the battery tray, terminals and connectors and smear the latter with petroleum jelly. Unless sealed for life, remove the battery vent plugs or strips and shine a torch into each cell to check the liquid level, which should cover the top of the plates. If the plates are exposed, top up with distilled or de-ionised water ONLY. A digital voltmeter is the easiest way to check the voltage across the battery terminals.

The following chart is an approximate guide to the state of a battery. Green indicates a good level of charge and is key to a long-lived battery. Orange shows that you should charge your battery soon to avoid any damage or loss of power. If your battery has been left in red for a few days you may have already permanently damaged it. You can see from the above that batteries require a lot of TLC. If they receive care then they will serve you for years – with good holding charge capacity.