Why Should Only New Batteries Be Charged in Pairs?
When you have a battery charger that specifies charging batteries in pairs, it might seem counterintuitive. Does this mean you cannot mix old and new batteries? What's the scientific reasoning behind this? Let's delve into the details.
The Science Behind Battery Voltage
The primary reason for charging pairs of new batteries is rooted in the principles of chemistry and physics. As a battery discharges, its voltage naturally drops. This discharge causes old batteries to become a lower voltage relative to the new ones. When you try to charge a single old battery with a new one, the new battery tries to charge the old battery, which can lead to several issues.
Damage to Non-Rechargeable Batteries
If you mix old and new rechargeable batteries, the situation becomes even more complex. The energy from the new battery cannot find an appropriate pathway to complete the circuit, leading to inefficient energy conversion and potentially the breakdown of the non-rechargeable battery. This inefficiency results in wasted energy in the form of heat.
Over time, when multiple old and new batteries are combined, you might end up with two dead batteries, leaving you in the same position you started with. This is why it's crucial to pair batteries of the same age and state of charge.
Heat Generation and Safety Concerns
In extreme cases, such as with lithium batteries, the excessive heat generated from mixing can cause a short circuit with minimal resistance. This leads to a substantial flow of current and the potential for fires. Lithium-ion batteries, in particular, have very low internal resistance when short-circuited, making them particularly dangerous when mixed with varying states of charge.
Why Most Devices Use Multiple Batteries?
Another common question is why most electronic devices use two or more batteries instead of just one. The answer lies in the fundamental properties of battery chemistry.
Battery Chemistry and Voltage Potential
Most battery chemistries, whether rechargeable or non-rechargeable, have a specific voltage potential. Rechargeable batteries typically have a voltage potential of 1.5V or 1.2V, whereas non-rechargeable batteries might have a slightly higher or lower voltage, often 1.5V for AA batteries. However, many electronic components require a higher voltage to function properly.
LED Lighting Example
Take LEDs for example. Most LEDs have a forward voltage drop of 1.7V or higher. If you try to supply LED lights with a voltage lower than this, they cannot function properly. Tiny indicator lights in devices also require sufficient voltage to work correctly.
In summary, the voltage in a battery is limited due to its chemical composition and cannot be increased simply by enlarging the battery or adding more chemicals. The voltage is only half of the equation for electrical power, with current also being a critical component.
Battery Stacking and Series Connection
To increase voltage, multiple batteries must be stacked together, typically in series. For instance, a watch battery and a AA or D battery both have the same voltage, circa 1.5V, but differ in the current they store and deliver. A 9V battery is simply six 1.5V batteries connected in series.
Practical Use and End-user Convenience
Another practical reason for using two batteries in many devices is their longevity. Two batteries will last longer than one, and if space is available, it's a logical choice. While using a single bigger battery could solve the issue, it would lead to a thick and awkwardly shaped remote control, for instance.
Imagine a scenario where you have a TV remote that requires D batteries. If you had a single larger battery, it would be impractical in terms of shape and size. Even if you could make a flat, disposable battery similar to a 9V battery, it would be more expensive to manufacture, leading to an increased cost for end-users.
To avoid the hassle of sourcing specialty batteries and the inconvenience of having to replace batteries as soon as they run out, manufacturers opt for existing battery types. This approach not only simplifies the manufacturing process but also ensures compatibility with a wide range of devices, enhancing user convenience.
In conclusion, the practice of charging batteries in pairs and using multiple batteries in devices is based on sound scientific principles and practical considerations. It ensures optimal performance, safety, and user convenience.