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Spotlight on directions!
Let's take the case of a battery with the following characteristics:
- Rated voltage: 12 volts
- C20 capacity: 90 Ah (20-hour discharge at 25°C)
- C100 capacity: 104 Ah (100-hour discharge at 25°C)
- Cycle resistance: 80% discharge 500 cycles, 50% discharge 750 cycles, 30% in 1800 cycles.
- Maximum load current: 18 Amps
- CCA 420A 5 sec.
Rated voltage expressed in Volt
Lead-acid batteries are made up of cells, each delivering a voltage of 2.1 V. These cells are connected in series to achieve the usual voltages required, usually 12 V, i.e. 6 cells. For 24 or 48 V systems, 12 V batteries are connected in series.
Advice : Never mix old and new batteries in the same park. The weaker the battery, the weaker the whole!
Capacity, expressed in Ampere hours
This is the number of amperes contained in a battery. When we install a set of 12 V batteries to add up their capacities (this is called a battery bank), we install them in parallel. If you install them in series, the voltages are added together, transforming 2 12 V batteries into a 24 V battery bank.
In the case of a parallel circuit, the sum of the capacities represents the theoretical size of the on-board "electricity reservoir". A theoretical capacity, because only 50% of it can be used without causing irreversible damage to your fleet. It's the C20 capacity that is commercially used to compare battery capacities, in this case 90 Ah.
Maximum starting current (CCA)
CCA stands for Cold Cranks Amps. This is the maximum current that can be drawn from a battery over a short period, e.g. when starting an engine. In this case, our battery can deliver 420 A for 5 seconds.
this is important information when choosing a battery to be used to start a combustion engine.
Discharge speed
Expressed in C10, C20 or C100, it indicates a battery's capacity as a function of its rate of discharge. What does it mean?
- C100 = 104 Ah, which means that our battery can supply 1.04 A for 100h (104/100).
- C20 = 90 Ah means that our battery can supply 4.5 A for 20h (90/20).
This information is essential for choosing a battery to be used for servicing. But unfortunately, not all manufacturers offer the same data, making it much more difficult to compare different brands.
Number of cycles
For a battery, a cycle represents a discharge followed by a charge. But the number of cycles depends on the depth of discharge. In the case of our battery :
- 500 cycles at 80% discharge
- 750 cycles at 50% discharge
- 1800 cycles at 30% discharge
Here we see the immense impact of deep discharges on battery life. Our Gel battery will only withstand 500 cycles at 80% discharge.
All these parameters have a major impact on the choice and durability of a fleet of new batteries for your boat.
