A STARTING BATTERY is designed and built to start a modern, high compression petrol or diesel engine whatever the engine application (for example marine, car, truck, motorcycle). Starting an engine requires a surge of power for a very short time and the starting battery will typically be discharged by less than 5% during a starting process. Starting batteries are built using a large number of thin plates for maximum surface area.
Once the engine is started, an alternator typically quickly recharges the battery during travel and it is ready to start the engine again.
An important performance measure of a starting battery is its cranking capacity (CCA) which needs to be matched to the engine or engines being started. Starting batteries are commonly described by the battery technology or ‘chemistry’, the most common being lead acid batteries which comes in two basic types:
- Flooded (or wet-cell) lead acid. Liquid acid requires maintenance and an upright position
- Sealed lead acid (SLA). Described also as Sealed maintenance free or Valve regulated lead acid (VRLA)
VRLA variants include Absorbed Glass Mat (AGM) and Gel. Both AGM and Gel have no free acid so are spill-proof and don’t need topping up with water. AGM and Gel batteries are safe for various orientations and limited ventilation and are ideal for caravans, 4WDs, boats and motorcycles where vibration resistance and high safety levels are key selection factors.
Latest technology starting batteries include Lithium (eg LiFePO4) batteries. These batteries are high performance, light weight, spill-proof and maintenance free with extremely low self discharge. LiFePo4 is ideal for infrequently used motorbikes and jet skis or for racing and marine applications where light-weight, impact resistance and fast charging is critical.
A DEEP CYCLE BATTERY is designed and built to provide small amounts of power for a longer period of time. An example is powering a fridge or freezer or auxiliary lighting. Deep cycle batteries are built using solid, thicker plates which have less surface area than starting batteries but are more suitable for greater depths of discharge and prolonged power demand. Deep cycle batteries can be flooded or wet-cell in stationary, well ventilated applications but AGM or Gel is perfect for vans, 4WDs and boats as they can be safely placed in various orientations. Deep cycle batteries are sometimes described as ‘house batteries’.
Important performance measures of a deep cycle battery are:
•Ampere-hours (Ah) which need to be matched to the electrical energy consumption of the appliances being powered by the battery
•Cycle Life and Depth of Discharge (DoD)
In contrast to starting batteries, deep cycle batteries can withstand many cycles of discharge and recharge (discharging and recharging a battery’s energy is called ‘cycling’). Cycle life and DoD are directly related: greater discharge depths results in less cycle life. For example, a lead acid deep cycle battery may have 10,000 cycles at 20% DoD but only 1,000 cycles at 80% DoD. Deep Cycle lead acid batteries are commonly described by battery ‘chemistry’ similar to lead acid starting batteries but with ‘Deep Cycle’ added to the description.
Latest technology deep cycle batteries include Lithium (LiFeP04). These batteries have properties of a long cycling life and a greater DoD ability. The low weight of lithium batteries can be a very great advantage for marine, caravans, camping and 4WD dual battery use. Lithium batteries tolerate storage when partially charged and being ‘dry’, they are also spill-proof and maintenance-free.
Dual purpose batteries
If space or weight is very limited, a dual-purpose battery option is available to cover starting AND cycling. Most dual-purpose batteries however won’t start an engine quite as well as a purpose built cranking battery and won’t stand up to as many deep discharge/recharge cycles as a purpose built deep-cycle model
Caution:
For marine and 4WD use, a starting battery can be drained by use of lights, stereo, radios and appliances. The result may be not enough power left in the battery for starting purposes. This can be dangerous on the water and in remote locations.
If possible, it is good practice to have separate starting (cranking) and deep-cycle batteries especially for critical applications.
If a dual purpose battery for high starting and moderate deep cycle service is a necessary compromise, it is recommended to choose and size a dual purpose battery with expert advice. Contact us should advice be needed.
