Most everyone has used rechargeable batteries at some point. Between lithium-ion, NiMH, and Ni-Cd batteries, we have many options available, and each kind has its merits. One of them, NiMH, offers long-lasting power and can be reconditioned when the ravages of time find them performing poorly. Let’s take a look at how to recondition NiMH batteries, how they work, and precisely what that battery reconditioning entails.
Table of Contents
What are NiMH batteries?
NiMH is the chemical abbreviation for nickel-metal hydride. In a battery, these elements combine to make a rechargeable battery. While there are several different kinds of rechargeables, NiMH batteries hold more power than some other kinds, including Ni-Cd batteries, or nickel-cadmium batteries.
In general, NiMH batteries hold more charge and last longer than NiCds. They also don’t have the terrible “memory effect,” which happens when you charge a battery before it’s completely dead and it starts to charge less and less.
Your NiMH batteries will hold lots of power and can run many of your daily essentials, including:
- digital cameras
- power tools
- video games
- electric toothbrushes
Why You Should Recondition NiMH Batteries?
Because of some complicated chemistry (if you’re interested, there’s some mind-boggling stuff here), NiMH batteries eventually run down. Inside the battery, dendrites grow, and when they do, they cover up some of the active materials.
In addition to creating a short inside the battery, the dendrites hinder and eventually prohibit charging, and it’s at that point that most of us throw them away and get more.
For the record, while spent NiMH batteries do not fall under the designation of hazardous waste and you are legally allowed in most states to throw them away, you shouldn’t.
Nickel, in large quantities, can harm the environment and the people and animals in it. It has been shown to have carcinogenic properties (but not when it stays inside the battery, so don’t think your GameBoy is giving you cancer), so if you can recycle your NiMH batteries, you should. Among other such businesses, BestBuy takes batteries in for recycling, and we all know where our nearest BestBuy is.
Anyway, you should recondition your batteries because they will last longer. This will save you money since you won’t need to buy more just yet, and it will be good for the world since there will be that much less waste produced by not throwing batteries away, buying new ones, and then throwing the packaging away, too.
There’s also the scientific argument: you should recondition your NiMH batteries because you can. I mean, why else do we try things?
How to Recondition NiMH Batteries
Figuring out how to recondition NiMH batteries is not difficult at all, and there are two ways to do it, each completely doable by even the un-handiest among us.
The Pump-and-Dump
This method on how to recondition NiMH batteries requires no equipment other than the batteries and their charger. It’s simple enough that you might try it first to see what you can do with it in terms of recharging your batteries. Then, if it doesn’t work, try our next method.
To use the pump-and-dump method:
- Insert your NiMH batteries into their charger and allow them to charge completely. The safest thing to do is let them charge overnight so you know they have fully and completely charged.
- Install the batteries in any device or gadget and let it run until the batteries fully discharge.
- Do this entire process one more time.
- Once you’ve recharged your batteries after discharging them completely the second time, they should be good to go.
The Jump
The Pump-and-Dump may not break loose all the dendrites inside your NiMH battery, in which case you’ll need to try something else. The Jump is so-called because it works on the same principle as getting a jump start for your car battery when it dies.
- Using a voltmeter, check the NiMH battery voltage. If the meter shows it’s completely dead, then it’s time to give this a shot.
- Get a NiMH battery of the same size and power, and be sure it’s fully charged (hopefully, in your set of NiMH batteries, only one needs reconditioning, and one of the others functions perfectly and can charge completely).
- Attach the two batteries. They’ll need to form a circuit, so you’ll need to connect the positive terminal of the fully charged battery to the positive of the dead battery, then connect the negative terminals in a similar manner. Two strips of metal will be ideal—stand both batteries up on one piece of metal and lay the other piece over the top of both batteries.
- Hold them here for 30 seconds.
- Check the battery you’re hoping to recondition with the voltmeter. Previously, it read “0.0.” If it reads any number at all other than that one, you’ve brought it back from the dead.
- If at first it doesn’t succeed, try at least one more time before giving up.
- Once the battery in question shows any charge at all on the voltmeter, place it on its standard charger and let it refill.
Tips to Maintain a NiMH Battery
Most of us had a dad or a granddad who dinned into us one phrase about being a responsible adult: “If you take care of your things, your things will take care of you.” NiMH batteries are things, so they need some care if you want to get the most out of them.
Fully Discharge Your Batteries
Not every time, but several times a year, be sure to run your NiMH batteries utterly down so that they’re totally discharged. Follow this up with a long (overnight?) stay in the battery charger so you can be sure they’ve fully recharged.
On the other hand, you shouldn’t run your batteries completely dead every single time you want to charge them, as this can put a strain on the electrolytes inside.
Room Temperature
Your NiMH batteries are not for your subarctic journey, nor should you rely on them while in the desert, because extreme temperatures are not these batteries’ friends. They don’t work great in extreme temperatures, so it follows that they don’t charge great there, either.
Don’t Mix and Match
Due to how chargers send power into the batteries they’re charging, if you mix batteries of different capacities into the charger, all the batteries will receive the same charge. This can create a problem if one of the batteries is sufficiently lower powered than the other. The weaker battery can get more power than it’s intended to handle, which can result in the battery heating up and even exploding.
If you have a smart charger, this is less of a problem, but in general, don’t mix batteries of different types, sizes, and capacities in the same charger.
Once They’re Charged, Use Your Batteries
FAQs
There are as many NiMH questions as there are products that can use NiMH batteries, so let’s look at some of the more common questions people have about them.
Can You Revive NiMH Batteries?
Yes, you can. Follow the above steps outlined in “The Pump-and-Dump” or “The Jump” above. If your batteries are salvageable, these are the ways to go about it.
Are NiMH Batteries Better Than Lithium Batteries?
Also, lithium batteries cannot be allowed to discharge fully without risking damage. However, NiMH batteries have a higher rate of self-discharge, losing about ten percent of their capacity per month, which means that for something like a clock, NiMH batteries would be inefficient.
How Long Do NiMH Batteries Last?
Generally, NiMH batteries can last through up to 1,000 charging cycles. If the batteries aren’t regularly used and charged, this number will be lower.
How Do I Test My NiMH Battery?
Using a multimeter or voltmeter is the most reliable way of testing. If your battery, tested when fully charged, shows a reading of between 1.3 and 1.5 volts, it is fully functional. Readings below 1.3 volts indicate a battery functioning at less than an optimal level, and over 1.5 volts means your battery is overcharged.
Can You Overcharge NiMH Batteries?
Yes, you can. Overcharging occurs when the battery’s positive electrode has run out of nickel hydroxide, which is required to react with the hydroxide from the electrolyte in the battery. When there’s no nickel hydroxide involved in the chemical process inside the battery, excess oxygen builds up in the battery.
This can create pressure in the battery, which can in turn force the electrolyte out of the battery, rendering the battery completely non-functional.
How long do NiMH batteries last if not used?
Generally, NiMH batteries will last about five years or so. However, this is for batteries that are used and recharged regularly. Batteries in storage will be much more likely to develop dendrites, not to mention that self-discharging phenomenon we’ve already discussed.
The short answer is that NiMH batteries are the ones you want for daily use. Need batteries to sit unused in your go-bag until the zombie apocalypse? Look elsewhere.
The Takeaway
Nickel-metal hydride batteries bring rechargeable technology to your gadgets and electronic gizmos, and they don’t suffer from the memory effect that so many of us ran into in the early days of rechargeables. They hold an average of 2200mAh, which will run your Nintendo Switch for a good, long while.
When they stop holding a charge like they used to, you have the option of reconditioning them, which you should at least try before trotting out to spend more money on new ones. Use the Pump-and-Dump or Jump techniques as described above to extend the life of your NiMH batteries. When cared for properly, these rechargeables will serve you well and for a long time.
James is an engineer and a professional blogger. He has gained extensive experience over the years, handling all types of power projects. He loves to share his experiences with all things related to batteries, generators, and other power-related topics.
