Debunking Common Battery Myths


It can be challenging to separate fact from fiction when it comes to batteries. You’ve probably heard all kinds of myths and legends about using, charging and storing batteries and been left wondering if they were actually true. 

Well, wonder no longer! Today, we cut through the noise and get to the truth behind common battery myths. You might be surprised to learn which long-held beliefs about batteries are entirely false. 

Your Battery Needs to Hit Zero Before Charging

This one has been around for a while, and like many myths, it does have its basis in a kernel of fact. With older nickel-cadmium or nickel-metal hydride batteries, there was a real chance that not being fully drained before charging would cause the battery to “forget” its capacity and lose its ability to fully recharge. 

But that isn’t the case with modern lithium-ion and lithium-polymer batteries, which are widely used in cell phones and other devices. Though they do tend to lose capacity a little bit with each charge, the amount is negligible and not impacted by how fully they are discharged. Even today’s nickel-metal hydride (NiMH) batteries do not need to be fully discharged. 

Keeping Batteries in the Freezer Makes Them Last Longer

Should you keep your batteries in the freezer? That’s a hard “no.” This common battery myth probably stems from the fact that high levels of heat can harm batteries. True as that might be, extreme cold isn’t exactly helpful. Rechargeable batteries including NiMH and lithium ion batteries do not respond well to wild fluctuations in temperature.

And that’s without even considering that being taken in and out of deep-freeze will expose batteries to a lot of moisture in the form of condensation. Our final ruling on this is that batteries should be stored in a cool (not cold), dry place. The temperature range that is generally considered to be “room temperature” is just fine. 

It’s Dangerous to Overcharge Your Battery

We’ve heard that overcharging batteries can cause all manner of mishaps, from wrecking the batteries and diminishing their storage capacity to causing them to overheat or even explode. In reality, this isn’t something you need to worry about. While overcharging is possible from a strictly technical standpoint, there are ample safeguards in place to prevent this from happening. 

Modern lithium ion and NiMH rechargeable batteries have built-in circuitry to prevent them from being charged beyond capacity, and battery chargers are also made with failsafes that will shut them off in case of overheating or overcharging. At the end of the day, as long as you’re using the right battery with the appropriate charger, and both the battery and charger are in good working order, there is no risk of overcharging. 

You Can Test batteries by Dropping Them

The theory is that you can test how full a AA or AAA cell battery is by dropping it on the floor and seeing how high it bounces. There actually is some truth to this, but only with certain batteries, so before you start dropping batteries left and right, make sure you know what you’re doing. Most importantly, this only works with alkaline batteries. Attempting to test lithium or other types of batteries this way will only damage your batteries. 

To test an alkaline battery, drop it onto a hard surface from a height of about 2 feet, letting its flat negative side hit the floor. If the battery is new and full, it will bounce. If not, it will hit the ground with a thud and stay there. 

Rechargeable Batteries Should Be Stored at Full Charge

You might have heard that you should always charge batteries fully before putting them away for long term storage, or perhaps even the opposite—that rechargeable batteries should be stored empty. Ultimately, neither is the case. For most batteries, the truth lies somewhere in-between. It is generally recommended that both lithium-based batteries and nickel-based batteries should be stored at 40% to 50% charge. 

This will prevent capacity loss while in storage, while also allowing for some inevitable self-discharge over time. That being said, it’s not important to hit an exact number. Lithium batteries should generally be stored as close to 40-50% as reasonably possible, but nickel batteries are less demanding. Storing them as much as 80% full is just fine, and they can also be stored completely empty with no apparent ill effects. 

You Can Recharge Alkaline Batteries

We’re not talking about actual rechargeable alkaline batteries here. Those do exist—they were first introduced in the 1970s and even had their own chargers—but these days are seldom used and hard to come by. No, we’re talking about putting single-use alkaline batteries in a charger intended for rechargeable batteries. 

The short answer is: don’t do this. The longer answer is that some people do it, and it may recharge your old disposable batteries to a limited degree. But they can only be recharged partially, only a handful of times, and not without some serious risks. Being improperly recharged can cause gas to be produced within the sealed battery canister, leading to leakage and rupture that can be harmful to both yourself and any device you put the batteries in. 

Myths That Are Actually True

Just as there are many long-held beliefs about batteries that turn out to be myths, there are also some so-called “battery myths” that are completely true! These are some of them. 

You Shouldn’t Mix Battery Brands

It sounds like something a marketing team cooked up to keep you from buying other brands of batteries, but this is generally true. Mixing batteries in any way—capacity, charge, type, brand—is generally not a good idea. Where brand is concerned, the reason for this is that same-sized batteries from different brands may have different chemistries and voltage, and mixing them can reduce performance. 

Batteries Should Be Charged 100% the First Time

You might have heard that batteries should “never be charged 100%” or “always charged 100% to avert some kind of disaster. Neither is true, but it actually is true that a battery’s first charge should be to 100%. This is true of both lithium and NiMH batteries. An initial charge of 100% will help set up the battery correctly and allow them to reach peak performance and capacity.

9V Batteries Can Start a Fire

Yep, they sure can. Because the positive and negative posts are on top, 9V batteries can spark or start a fire if the two poles come into contact with a metal object. This can happen when the batteries are in storage, bumping around your junk drawer, or even mostly-discharged in the trash. Long story short, store 9V batteries in their original packaging and cover the poles with electrical tape when you throw them out. 

Keeping Batteries in a Device Will Drain Power 

This is true. Granted, all batteries have at least some self-discharged whether they are stored in a device or not. But they’ll run out faster if you leave them in, even if the device in question is not used. If you have rarely-used devices that take batteries, best practice is to take the batteries out when not in use and store them separately.