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Charging and discharging batteries
Intermediate
Capacity, internal resistance and efficiency.
Capacity (Ah) is how long a battery can supply current; real capacity is lower at high currents. Charging needs a voltage above the battery's EMF; efficiency is <100%.
2000 mAh at 100 mA lasts about 20 h.
Deep discharging shortens lifetime.
In more detail
Charging a rechargeable battery reverses the chemical reaction by forcing current through it. Charge and discharge cycles reduce capacity over time as materials degrade.
Real-world uses
- Electric vehicles rely on charging and discharging lithium-ion batteries.
- Smartphones use charge controllers to protect batteries.
- Phone users notice that a battery holds less charge as it ages, because its capacity falls and its internal resistance rises.
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Frequently asked questions
Why do batteries lose capacity?
Chemical side reactions and structural changes gradually reduce the usable charge.
Should I fully discharge a battery?
Usually not, since shallow cycles tend to extend battery life.
What is battery capacity?
The total charge a battery can deliver, often quoted in ampere-hours.
Related topics in Current Electricity & Circuits
Faraday's laws of electrolysis · Thermoelectric effects · Batteries · Electric circuits symbols · Short circuit · Series vs parallel in homes