In the previous chapters, we learned about battery capacity, Watt-hours, and C-rating. Before we start exploring different battery types, let’s look at a few more battery terms that you’ll often come across in datasheets and product specifications.
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Understanding these terms will make it much easier to choose the right battery for your electronics projects.
Charging current
The charging current is the current used to charge a battery. Every battery has a recommended charging current and a maximum charging current specified by the manufacturer.
Charging a battery with excessive current can generate excess heat, reduce its lifespan, and, in some cases, permanently damage the battery.
For example, when you connect your smartphone to a charger, the charging circuit inside the phone controls how much current flows into the battery.
Charging voltage
Every rechargeable battery also has a maximum charging voltage.
To charge a battery safely, the charging circuit must raise the battery voltage to this value and then carefully control the charging process.
For example, a typical lithium-ion cell has a nominal voltage of 3.7 V but is fully charged at about 4.2 V. Although a USB charger may provide 5 V, the battery is not connected directly to it. Instead, a charging circuit regulates both the voltage and current before charging the battery.
Shelf life
Sometimes batteries remain unused in shops or storage for months or even years before being used.
The shelf life of a battery refers to how long it can be stored while still retaining most of its usable capacity.
Even when not connected to a device, batteries gradually lose charge over time due to a phenomenon called self-discharge. Different battery chemistries have different shelf lives, with some retaining their charge much longer than others.
Cycle life
Rechargeable batteries can only be charged and discharged a limited number of times.
One complete charge and discharge is known as a charge cycle. The total number of charge cycles a battery can complete before its capacity falls to a specified level—typically around 80% of its original capacity—is called its cycle life.
In general, a battery with a higher cycle life lasts longer and provides better value over its lifetime.
Energy density
The energy density of a battery tells us how much energy it can store for a given weight or volume.
It is commonly expressed in watt-hours per kilogram (Wh/kg).
A battery with a high energy density can store more energy without becoming significantly larger or heavier. This is one of the reasons lithium-ion batteries are widely used in smartphones, laptops, and electric vehicles.
Power density
While energy density tells us how much energy a battery stores, power density tells us how quickly it can deliver that energy.
Power density is commonly expressed in watts per kilogram (W/kg).
A battery with a high power density can supply large amounts of current in a short time, making it suitable for applications such as power tools, drones, and electric vehicles.
Energy density vs power density
Although these two terms sound similar, they describe different characteristics of a battery.
A battery with high energy density stores a large amount of energy and can power a device for a longer time. A battery with high power density can deliver that energy very quickly.
For example, a smartphone battery has a relatively high energy density because it needs to power the phone for many hours. However, it is not designed to deliver extremely large currents instantly.
A capacitor, on the other hand, stores much less energy than a battery but can release that energy almost instantly. This gives capacitors a much higher power density than batteries, which is why they’re used in applications such as camera flashes and pulse power circuits.