How do you choose the right battery and charger for low-voltage and low-current hardware projects?

2 Battery size and capacity

The size and capacity of your battery depend on your project's power requirements and physical constraints. You need to calculate how much current your circuit draws, how long you want it to run, and how much space you have for the battery. The current rating of a battery is measured in milliampere-hours (mAh), which indicates how much current the battery can provide for one hour. The higher the mAh, the longer the battery will last. However, the mAh also depends on the discharge rate, which is the ratio of the current to the capacity. The higher the discharge rate, the lower the actual capacity. You can use online calculators or datasheets to estimate the battery life for your project.

3 Battery chemistry

The chemistry of your battery affects its voltage, performance, and safety. The voltage of a battery is determined by the electrochemical reaction between the anode and the cathode materials. The nominal voltage of a battery is the average voltage during discharge, while the cut-off voltage is the minimum voltage below which the battery should not be used. The voltage of a battery also varies depending on the temperature, load, and state of charge. You need to choose a battery that has a voltage range that matches your circuit's operating voltage. For example, if your circuit needs 3.3V, you can use a lithium-ion or lithium-polymer battery that has a nominal voltage of 3.7V and a cut-off voltage of 3.0V.

4 Charging circuit

To recharge your battery, you need a charging circuit that can supply the appropriate current and voltage to the battery terminals. The charging circuit should also have protection features to prevent overcharging, overdischarging, short-circuiting, and overheating of the battery. The charging method and parameters depend on the battery type and chemistry. For example, lithium-ion and lithium-polymer batteries require constant current and constant voltage (CC-CV) charging, while nickel-metal hydride (NiMH) and nickel-cadmium (NiCd) batteries require constant current (CC) charging. You can use dedicated charging modules or ICs that are designed for specific battery types and have built-in protection circuits.

5 Testing and monitoring

Before using your battery and charger in your project, you need to test and monitor their performance and behavior. You can use a multimeter, an oscilloscope, or a battery tester to measure the voltage, current, capacity, and internal resistance of your battery. You can also use a thermocouple or a temperature sensor to measure the temperature of your battery and charger. You should observe how your battery and charger respond to different load conditions, ambient temperatures, and charging cycles. You should also check for any signs of swelling, leaking, or smoking of your battery and charger.

6 Best practices

To ensure the safety and reliability of your battery and charger, you should adhere to some best practices when designing and using them in your project. This includes choosing a battery and charger that are compatible with your circuit's voltage and current requirements, using a battery holder or connector that matches the polarity and size of your battery, incorporating a fuse or diode to protect against reverse polarity or overcurrent, installing a switch or MOSFET to control the power flow to your circuit, adding a voltage regulator or buck converter to step down the battery voltage to your circuit's operating voltage, incorporating a low-voltage detection or low-battery indicator to warn you when recharging or replacing is necessary, using a balancer or protection board for equal charging and discharging of multiple cells in series or parallel, storing your battery in a cool, dry, ventilated place away from heat sources, metal objects, and flammable materials, and disposing of your battery properly according to local regulations and environmental standards.

7 Here’s what else to consider

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