Understanding battery ratings
Lead acid batteries like this 68MF automotive battery or Seafarer 780 have a multitude of multitude of battery ratings listed across the top. But how do we make sense of them, and do they really matter? Let’s take a look.
These are generally found on the top of the battery the first on and the most common in the automotive industry in CCA or Cold Cranking Amps. This is the measurement of the battery’s ability to deliver current over a 30-second time period whilst also maintaining a minimum of at least 7.2 volts. The test is performed at a temperature of -18 degrees Celsius. Starting your car in the Australian alps, in winter, at 4am in a blizzard – negative 18 is pretty much a temperature you’ll never encounter in this country. But, it is still an indication that you can use to compare the starting power of one battery to another.
Secondly is MCA or Marine Cranking Amps, As the name suggests, Marine Cranking Amps is a rating used almost exclusively for boat batteries. This test is essentially exactly the same test that is performed for CCA, except it is tested at 0 degrees Celsius, instead of negative 18. And that is why you will find the MCA rating on Marine Batteries higher that the CCA – the chemical reactions which are taking place within the battery increases the warmer the ambient temperature is.
The third rating you’ll see is RC or Reserve Capacity. This measures the amount of time in minutes that a fully charged battery can deliver 25 amps of power, without dropping below 10.5. This test defines the length of time you could theoretically drive a vehicle after its charging system has failed, and the vehicle is instead relying on the reserve capacity of the battery to power everything. For example a battery with a RC rating of 55 would give you almost an hour of power in this situation.
Next up, the Ampere Hour or Ah rating is slightly more confusing. This is the rating used for Deep Cycle batteries used in the recreational market. This rating represents the steady flow of current the battery will deliver for a period of 20 hours, without dropping below 10.5 volts. A simpler way to think of this is, a battery with a 100Ah rating can deliver 5amps of current over a 20-hour period. You can also substitute these figures so long as they still multiply together to equal the Ah rating. So instead of 5 amps over 20 hours, it could be 10 amps over 10 hours, or 20 amps over 5 hours. You can use these figures to work out how many hours you can run your 10-amp camping fridge, or 5-amp lighting setup.
The next time you’re in the market for an automotive starting battery, a battery for your boat or even a deep cycle battery for your next camping trip away – you’ll be a bit more educated when it comes to how these things are rated, and it might just help you choose the best one to suit your needs.
For more expert tips and battery advice, come in-store and speak to one of our local battery experts!