Rechargeable batteries, like these high-quality Eneloop ones from Amazon, offer a number of important benefits to our electronically-enhanced lifestyles. One is to our pocketbook; as the need to buy disposable batteries reduces, we save money. Another is to our environment, as fewer of those toxin-containing disposables head to the landfill. Since there is easy access to both kinds, is it smart to mix and match them?
You should not combine rechargeable and disposable batteries in the same device. While batteries of the same size look very similar, disposable and rechargeable batteries are made of different materials with different electrical charicteristics. The mismatched voltage can damage the batteries and the equipment they’re used in.
If your need for juice is immediate and short-term, mixing the two different types won’t present a problem right away, and the receiving electronic device should work normally without incurring any damage. Just be sure to remove the mismatched batteries, and replace them with fresh batteries of a matching type as soon as you can. You can do this in a pinch, but don’t do it for days or weeks at a time.
How Rechargeable Batteries Work
As we’ve discussed elsewhere on the site, all batteries work because of an electrochemical relationship between two different materials. One material, called the anode, has a quantity of “free” electrons that it wants to get rid of. The second material, the cathode, desires electrons. If these two materials are connected to each other by a wire or an electrical circuit, the electrons flow, creating electricity.
Traditional disposable batteries, like the common Energizer brand (on Amazon), have a fixed quantity of free electrons. When all of these electrons find their way from the anode to the cathode, the battery ceases to have any electrochemical potential, and the battery is pronounced “dead.” Disposable batteries are typically combinations of carbon and zinc, lithium, potassium hydroxide, and manganese dioxide.
Why you Shouldn’t Mix Rechargeable and Non-Rechargeable Batteries
Rechargeable batteries have a fixed quantity of free electrons also, but these electrons can be, with a little push from the appropriate battery recharger (emphasis on ‘appropriate’ – our guide on why), returned to the anode. This key difference is due to the different chemical material makeup of the two kinds of batteries. Nickel, cadmium, lithium-ion composites, and metal-hydrides are common rechargeable materials.
The point when a battery is “dead,” and has no more available free electrons is called its terminal voltage. Nearly all disposables have a higher terminal voltage than their rechargeable counterparts. This is why rechargeable batteries tend to die sooner. Electrochemically, dead batteries have moved all of their once free electrons to the cathode.
When rechargeable and disposable batteries are placed together on the same circuit, the disposable battery will have a higher terminal voltage. As they create the flow of electricity, the rechargeable battery will run out of free electrons first. When this happens, the disposable battery will electrically demand that the rechargeable battery give up electrons that it does not have.
In this case, the rechargeable battery will enter a state called “over-discharged.” If this condition goes on for long enough, and at a sufficient electrical intensity, the rechargeable battery will begin to heat up and over time can physically degrade. Under the right conditions, this can result in the battery leaking material, which can destroy the battery and possibly damage the device.
Other kinds of batteries can become over-discharged as well. This is often caused by mixing different types or ages of disposable batteries together (more on this in our guide) . When alkaline batteries are over-discharged, acidic and hazardous material can leak out of the battery. Some over-discharged rechargeable batteries will sometimes leave a fine, easily cleaned, white powder behind.
Why You Shouldn’t Worry If You Do Mix Rechargeable And Non-Chargeable Batteries
Damage by mismatched batteries can lead to problems, but it usually takes an amount of time for this to happen. If the device you’re needing to power requires batteries but you only have a mismatched set to choose from, using this collection for a short amount of time very likely will not damage the device or the batteries.
This is largely because the main negative effect on over-discharged batteries is excess heat. The heat takes a length of time to build up, due to the structure of the battery and the relatively low power draw from its less terminal neighbors. In turn, it takes a decent amount of heat to ultimately deform and damage the device those batteries are in. But, you don’t get to choose when this problem occurs…it will happen sometime after the mixed batteries start being used together, but it’s hard, even foolish, to try to predict when and time it “just right.”
How to Prevent Damage to Rechargeable Batteries
Changing the batteries as soon as possible, when using mismatched types of batteries, will also ensure that the rechargeable batteries mixed in with the lot will not incur damage (more on preventing rechargeable battery damage in our guide) . That same tendency to build up heat while being over-discharged will be strongest with the rechargeables, and over time this can reduce and eliminate the capacity of the batteries to hold a charge.
When replacing the batteries, it’s also best to use all of the same brand, chemical type, and age. This will ensure that all of the batteries used in a device will have nearly identical terminal voltages, and it will be extremely unlikely to cause any of them to become over-discharged. Keeping your rechargeable batteries at a 40% or higher level of charge will help as well, since the mismatched voltage becomes more of a problem when rechargeable batteries are low on charge.