BATTERIES Continued on page 15
to 264V) if the equipment and battery pack are to be used abroad, as well as a waterproof (IP67) charger for rugged and outdoor applications. A charger with a temperature sensor may also be required if the application is operated in very hot or very cold temperatures.
Knowing the mAH / AH capacity of your battery is an important factor when deciding on the charging current. Such details are usually found on the battery label on the side or top of the battery. Most Li-Ion cells should not be charged above 1C and a when charged below 0.5C. The ‘C’ rating is simply the capacity of the battery – so for a 3.5Ah cell, 1C would be 3.5A and for a 10Ah battery pack, 0.5C would be 5A.
How do Li-Ion chargers work? charging sequence consisting of three different stages: constant current charging, constant voltage charging and charge completion. Each step ensures safe and battery from overcharge. Step 1 – Constant Current Charge: when the charger is connected to the mains and a battery is attached to the output, a charge cycle begins automatically. In this stage, the charger operates in constant current (CC) mode, supplying the maximum rated current. The charger’s LED indicator will display yellow during this process. This step allows the battery to charge rapidly, typically reaching 80 per cent to 95 per cent of its capacity.
Step 2 – Constant Voltage (Timer) Charge: once the battery approaches its upper voltage limit, the charger transitions to constant voltage (CV) mode. In this mode, the current gradually tapers off. At the start of this step, an LED indicator will change in CV mode until the current decreases to timer expires. By the end of this stage, the battery reaches full charge. Step 3 – Charge Complete: when the battery is fully charged and the current has dropped to zero, an LED indicator turns green. At this point, the charger may remain connected to the battery without risk. If the battery voltage later falls by more than 0.1V per cell, the charger will automatically initiate a new charge cycle.
Using your charger properly To maximise the performance and longevity of both your charger and battery, it is important to consider the following best
Figure 1: There are typically three main charging phases or steps. “
The sheer volume of charging standards, power varieties, cables terminology makes it the right charger
operating practices.
Firstly, avoid leaving an unregulated “automatic” charger connected to the battery overnight unless it shuts off Continuous charging under these conditions can stress the cells and reduce service life. Equally important is ensuring that the charge voltage never exceeds the voltage control prevents the formation of metallic lithium on the negative electrode, a condition that can degrade battery capacity and overall performance. Proper storage and operating conditions also play a critical role in maintaining battery health. This includes storing batteries in a well-ventilated area where the ambient temperature remains below 25°C. Exposure to higher temperatures accelerates aging, with every 5°C increase above 35°C causing Charging should also be avoided in extreme below 0°C or above 45°C, as this can
16 SEPTEMBER 2025 | ELECTRONICS FOR ENGINEERS ”
When planning a charging cycle, the total required time should be calculated carefully. As a general rule, divide the battery’s amp- hour rating by the charger’s current rating (in amps), then add an additional one to two hours to allow for top-off charging. For best results, the device should be turned off or disconnected from the battery during charging. A parallel load can interfere with the charger’s ability to reduce current correctly and may prevent the battery from reaching full capacity.
It is also important to note that not all chargers apply a complete topping charge. In some cases, the battery may not be fully charged even when the “ready” signal is displayed. To prepare a battery for storage, always ensure that it is partially charged. A state of charge between 40 and 50 per cent is considered ideal for minimising long-term degradation.
Finally, charge voltage adjustments should be based on the battery’s actual terminal voltage rather than the value assumed or interpreted by the charger itself. This ensures accuracy and helps avoid premature wear or incorrect charge termination. Studies have shown that charging at a slightly lower voltage can dramatically increase the number of cycles you can get out of a battery. Charging to 4.1V instead of 4.2V (which is the equivalent of charging to around 90 per cent) has been shown to add 50 per cent or more cycles to a battery over its entire life. To do this, you’ll need a higher-
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