Dual Battery Cradle Fitting Instructions
For many years the number of plates per cell was taken as a guide to the engine cranking power provided by the battery. However, over time this criteria proved to be misleading. Starting power is a function of the area of plate surface exposed to acid. If all plates were the same size (and therefore the same area) plates per cell would be a useful comparative guide. However, plate dimensions vary dramatically from one manufacturer to another. To overcome this difficulty, in1985 the Australian battery manufacturers adopted the SAE (Society of Automotive Engineers) standard for cranking capability. Under the SAE standard, battery cranking power is specified in CCA’s (cold cranking amps).
To make a valid comparison from one battery to another, it is absolutely vital for both battery performances to be quoted against the same standard test. Performances quoted at higher temperatures, shorter durations or to higher end voltages, can be manipulated so as to appear superior to SAE ratings.
ACCESSORIES POWER (AMP Hour Capacity)
The power available from a fully charged battery to operate accessories is a function of the weight of reactive lead contained on the battery plates, below the acid level. The weight of reactive material depends on the thickness of plates, area of plates below the acid level and the number of plates in each cell.
For many years the power available for accessories was quoted as ‘amp hours’. In the case of automotive batteries, the amp hour rating was a statement of the amps that could be provided continuously for 20 hours. Whilst the amp hour rating did provide a rough guide to the weight of reactive lead available, it completely failed to indicate the ability of the battery to power the full vehicle accessory load. Some battery distributors use less severe tests conducted at higher temperatures to disguise low performance batteries. The Australian Standard specifies a standard measure for reserve capacity.
The reserve capacity rating for a battery is an attempt to specify in minutes how long a battery could keep the vehicle running in the case of a complete alternator failure with a notional level of accessories in use.
COLD CRANKING AMPS (CCA)
The international recognised battery performance test: the discharge load in amperes which a new fully charged battery at 18C (0F) can deliver for 30 seconds and maintain a voltage of 1.2 volts per cell or higher.
RESERVE CAPACITY (Minutes)
The time in minutes that a new fully charged battery will supply a constant load of 25 Amps at 25°C without the voltage falling below 10.5 volts for a 12 volt battery and 5.25 for 6 volt battery.
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