The voltage of a fully discharged battery depends on the type of battery you're referring to. Different battery chemistries have different nominal voltages and different "discharged" or "empty" voltages. Here are some common examples:
1. **Alkaline Batteries (e.g., AA, AAA):** These typically have a nominal voltage of 1.5 volts. When fully discharged, they may drop to around 0.8 to 1.0 volts. However, they can continue to deliver a small amount of power even below this threshold.
2. **Lithium-ion Batteries (e.g., in smartphones, laptops):** These batteries generally have a nominal voltage of 3.7 or 3.8 volts per cell. A fully discharged lithium-ion battery might drop to about 3.0 volts or slightly lower. Discharging below this level can potentially damage the battery or reduce its lifespan.
3. **Nickel-Metal Hydride (NiMH) Batteries:** These have a nominal voltage of 1.2 volts. When fully discharged, their voltage might drop to around 1.0 volts or slightly lower.
4. **Lead-Acid Batteries (e.g., car batteries):** These typically have a nominal voltage of 12 volts. A fully discharged lead-acid battery might drop to around 10.5 to 11 volts. Discharging below this level can lead to sulfation and reduce the battery’s lifespan.
5. **Lithium Iron Phosphate (LiFePO4) Batteries:** These usually have a nominal voltage of 3.2 or 3.3 volts per cell. When fully discharged, they might go down to about 2.5 volts per cell.
Battery voltage can be a good indicator of its state of charge, but keep in mind that a battery’s performance also depends on its chemistry, age, and how it has been used.