How to Charge NiMH Batteries

This article was co-authored by wikiHow staff writer, Hunter Rising. Hunter Rising is a wikiHow Staff Writer based in Los Angeles. He has more than three years of experience writing for and working with wikiHow. Hunter holds a BFA in Entertainment Design from the University of Wisconsin – Stout and a Minor in English Writing.

There are 11 references cited in this article, which can be found at the bottom of the page.

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NiMH (nickel-metal hydride) and NiCad (nickel-cadmium) batteries are two of the most challenging batteries to charge properly and safely. These nickel-based batteries do not allow you to set a maximum charge voltage, so overcharging can result if you are unaware of the proper charging methods for nickel batteries. Learn how to charge NiMH batteries so you can avoid potential charging problems.

Using a Battery Charger

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  • NiMH battery chargers usually cost between $20–30 USD.

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  • You may need a screwdriver to access the battery compartment depending on the device.
  • If you aren’t sure how to access the battery in your device, check the instruction manual.

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  • Rechargeable batteries slowly lose capacity the more you use them, but your charger will still be able to detect the maximum charge it can hold.

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Slot or plug the batteries into the charger. If you have standard size batteries, such as AA, AAA, or D, look for the slot of the same size on the charger. Push the negative end against the spring so the positive terminal presses against the other side of the slot. If you have a battery pack with wires, plug it into the port on the side of the charger. [4] X Research source

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  • For example, if you have a battery with a 2,400 mAh capacity, then you would use a 240 mA C-rate on your charger.
  • Don’t charge your batteries in parallel since the current won’t be distributed evenly. [6] X Research source

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  • Avoid using a charger with only a timer if you don’t know the actual capacity of your battery since you could easily overcharge it.
  • The timer in your charger may reset if there’s a power surge or an electrical issue.

Tip: Some smart chargers will completely discharge your battery before it starts charging to prevent it from overheating or venting.

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  • Usually, charging at a 1C rate will take less than 2 hours to get a full charge.

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  • For example, if you have a 1,200 MHA battery and your charger outputs 100 mA, your equation would look like: (1,200 mHa x 1.2) ÷ 100 mA.
  • Simplify the parenthetical: (1440) ÷ 100 mA.
  • Divide by the C-rate: 1440 ÷ 100 mA = 14.4. So it would take 14 hours to fully charge your battery.

Charging and Handling Batteries Safely

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Charge your battery at room temperature. If you recently used the battery and it still feels warm, allow it to cool down before you start charging it. Keep the charger and battery away from direct sunlight or heat sources since it can make the battery overheat and affect the capacity. Avoid letting the battery drop below 10 °C (50 °F), or else it won’t charge effectively. [10] X Research source

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Unplug the charger as soon as your battery is finished charging. Avoid overcharging your battery since it will reduce the maximum capacity and it could overheat. Keep track of how long you’ve left your battery plugged in or watch the timer on the charger so you know how much longer you need to leave it plugged in. When it’s finished, disconnect the charger from power before taking your battery out. [11] X Research source

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Warning:It’s normal for your battery to warm up while it’s charging, but unplug it if it ever is too hot to touch since it could get damaged.

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  • Recharge your battery after 6 months if you haven’t used it.

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  • Many electronics stores have battery drop-offs. Simply take your battery into the store, find the drop-off box, and put your battery inside.

Community Q&A

It’s not a great idea unless you know what you are doing. But if it’s a functional pack you should be able to extract a functional cell. Be warned that packs may be made with cells that are not a typical consumer size, e.g. AA, and the contacts/terminals may be spot welded together. If you pierce the cells or damage a contact while disassembling, you could create a dangerous or just plain useless dead battery.

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If the light goes from red to green and is blinking, it indicates that it will be fully charged soon.

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How to Charge a Battery With a Solar Panel – Only 4 Steps

how to charge a battery with a solar panel

Charging your batteries using solar panels is an excellent method of utilizing clean, green, and renewable energy. However, how to charge a battery with a solar panel? Before you begin, you have to set up a charge regulator, which is for controlling the voltage from the panel that’s transmitted to the battery.

Without a regulator, on sunny days, the solar panel might generate more energy than your battery could manage, and this could cause damage to your battery. Fortunately, this is a straightforward approach that would have you charging your batteries quickly.

We’ll continue discussing the proper steps in using solar panel to charge battery in this post. So, let’s begin!

Table of Contents

Detailed Steps in Connecting a Charge Regulator to a Battery and Solar Panel


As mentioned, rather than attaching your battery directly to your solar panel, it’s fundamental to set up a charge controller between your solar panel and battery.

Materials and Tools Needed:

  • Battery charge
  • Solar panel
  • Inverter (required if you’ll utilize AC powered devices)
  • Charge regulator
  • Connectors, wires, and cable (usually contained in your solar panel kit)
  • Screwdriver
  • Wire cutter
  • Drill
  • 12V deep cycle battery
  • Electrical tape
  • Crescent wrench
  • Goggles (for eye protection)

Here are the things to do:

Step 1: Ready all the materials and tools required.

Install the solar panel so that you could connect it to the primary connector later on. Arrange the panel first to know if an extension is necessary or not, as this will depend on the setup.

Make sure that you cover the wires for additional protection. Do this first if the battery isn’t charged yet. It’s crucial to charge the battery before you install the panels to save time.

Then, see to it that the battery’s negative terminal is on one side, and the positive terminal is on the other side. You can continue to step 3 if your battery is already parallel.

Otherwise, you will need to cut your cables and create a few jumpers. Basically, it goes like this: the larger the inverter, the longer the cable.

Step 2: Attach the charge regulator into the lead battery.

There must be a wire on the charge regulator where you could clamp or attach the battery. You must switch off the inverter first; if the regulator is waterproof, you could put it anywhere; if not, ensure that you position it in a safe spot.

Step 3: Connect the lead battery to your inverter.

You can configure the battery as parallel to the other batteries in your solar system. Connect the batteries with cables when adding more of them. It’s essential that you link the cables to the correct terminals.

Make sure your inverter can charge numerous parallel batteries at once.

Step 4: Hook up the battery regulator to the solar panel.

Finally, you may run the line from the solar panel to the charge regulator to set it. An extension cord might be necessary to hook up the components, depending on your setup.

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To learn more about connecting a charge regulator with a solar panel and battery, you might want to check out this video:

How Long Does It Take to Charge a 12-volt Battery With a Solar Panel?

Depending on the size of your battery, it’d require approximately five to eight hours to fully charge car battery with solar panel that could generate 1 amp of current.

In addition, if you want to ensure a more effective charge, be sure that the solar panel is free from any obstruction and is positioned directly facing the sun.

Please note that charging time usually varies depending on the amp output and size of your panel. A large-sized panel could charge a car battery more quickly than a solar charger with a small-sized panel.

What Is the Required Solar Panel Size to Charge a 12-volt Battery?

A solar-powered car battery charger can commonly produce 13.6 volts up to 17.0 volts, depending on the model you pick. It is purposely designed to charge standard vehicle batteries and could run any 12V gadgets.

Solar chargers are ideal for small cabins, cars, recreational vehicles, and boats. Interestingly, some models come with a converter that is meant for charging smart devices. They are valuable investments for portable off-grid systems.

A regular solar panel measures 65×39-inches, and is utilized to charge a 12-volt 100W battery. On the other hand, the commercial solar panel measures 77×39-inches.

The Correct Way of Solar Panel Charging Car Battery

If you’re going for a DIY approach, ensure that your charging system has a charge regulator to control the voltage.

When using a solar charge regulator, you could attach one end of the controller to the battery. From there, you can attach the other end with your solar panel.

Such a method significantly aids in regulating the voltage so that your battery won’t exceed the safety limit. The charge regulator tracks the voltage of the battery, a process known as pulse width modulation.

Using a charge regulator can help keep the battery from going beyond the target limit or the safe float voltage. Luckily, it’s safe to leave this type of setup attached continually without worrying about the potentiality of battery damage.

The Stages Involved in Using a Solar Panel to Charge Car Battery


The four primary steps involved in charging a battery using a solar panel are as follows:

Stage 1: Bulk Phase

This is mainly the first phase of charging your battery using the energy from the sun. It begins when the sun shines or when you switch on the generator.

This stage will begin when your battery reaches a low-charge phase. This occurs when the charge is below 80 percent.

It is in this phase that the panel puts as many amps as probable into the battery cells. Moreover, the voltage in your batteries increases slowly as they take in the electricity.

Stage 2: Absorb Phase

This phase occurs when the charge level is between 80 to 90 percent.

Or, it emerges when your batteries reach a charge amounting to 14.4 up to 14.8 volts. Chiefly, when your batteries reach this charge percentage, it goes into the absorb phase, which generally relies on the charge rate. Fundamentally, the above charge rate is for lead-acid batteries.

This phase ends once the number of amps going in your batteries reaches a particular number that’s pre-set, or a predetermined time period elapses.

Stage 3: Float Phase

This phase commences when the charge regulator lessens the voltage to a particular pre-set value. It is accomplished when your batteries obtain a charge level of 100 percent.

You must be knowledgeable of how to program your charge regulator.

Stage 4: Equalization Phase

This phase refers to a regulated overcharge phase, which is accomplished regularly.

Equalization helps maintain lead acid batteries, whose capacity declines due to sulfation.

How to utilize a solar panel to charge a lead-acid battery?

The first thing you have to do is to invest in a premium quality solar panel and voltmeter. See to it that you choose a solar panel with the standard size.

When you attach the solar panel to your battery, see when the voltage reaches roughly 14-volt; this implies that your battery is fully charged.

Remove the connection when your battery is already fully charged. This is to impede charging the battery too fast or overcharging it. It’s vital that you carefully check your battery’s user manual to unveil the number of amps your battery can handle.

Meanwhile, if you are acquainted with trickle charging, keep in mind that there are a few solar chargers specifically engineered to sustain your battery’s charge level.

Such solar chargers don’t generate excessive voltage to impair your battery. For this reason, it is practical to get a trickle charger if you keep your car idle for an extended time.

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The Bottom Line

You learned from this post the detailed steps on how to charge a battery with a solar panel. Rather than directly charging the battery with a solar panel, it’s best if you use a charge regulator to ensure safety. This way, you can extend the lifetime and performance of your battery.

So long as the materials and tools required when charging your battery with a solar panel are prepared and you carefully follow the guides shared here, you’re good to go. Hopefully, you can enjoy the perks of solar energy just as much as we do. Please feel free to share this article if you find it useful.

Solar AA (NiMH) Battery Charger



By Deutschmann Follow

Recycled, multi-voltage solar panel

Resurrect Your Gamecube

Longboard Bike Carrier

Greetings! I got the idea from this when I got some small solar cells from a catalog. I had noticed that most chargers for Energizer NiMH (Nickel Metal Hydride) battery cells produced about 3 volts. The cells I used were one volt each, but you could use 1,5 volt cells too, or any individual call voltage, just so long as your total cell voltage was somewhere close to 3 volts. Less power would probably work too, but the cells might take longer to charge. Note that this is my first instructable, so it might be significantly less than perfect.

Step 1: Materials Needed

This is pretty simple, and you don’t need much. I haven’t tested it too extensively, and it’s possible that I might need to add diodes or something to allow the batteries to charge. I’ll try and post an update if that turns out to be the case.
1. Battery cases; any battery that is normally 1.5 volts (NiMH cells tend to be 1.2, which is close enough) should charge off this array. Do whatever is most practical for your needs; AAA cells, AA cells, C cells, or D cells, to name a few that would work.
2. Batteries; I used NiMH cells because they’re the lowest maintenance. They don’t have to be discharged completely, like NiCd (Nickel Cadmium) cells, and they’re widely available. You would probably need to modify the circuit if you wanted to charge another type of cell.
3. Solar array; I used three one volt crystalline cells fastened together into one big three volt array. I’m not sure if the three volt amorphous cells from portable calculators would work; You could try.
4. fasteners; I had a problem with the solar array falling apart, as it was made from three separate cells; I used two metal rails and some epoxy to keep them together. I also used foam tape later.

Step 2: Assemble the Solar Cell

Here we put the solar power supply together. If you have a solar cell that doesn’t need to be assembled like this, go right ahead and wire it up. If you’re using multiple cells, first, wire them in series, positive to negative. You can test them with a voltmeter to make sure the connections are good and the cell produces the required juice (3 volts, or somewhere close). Then make sure the cells stay together; I did that with Epoxy, but you can be creative.

Step 3: Battery Cases

Put the battery cases on the back of the array; as I’ve said, I attached them with foam adhesive tape. wire the cases together in parallel, or positive to positive, negative to negative. They’ll charge backwards and all kinds of funny stuff if you wire them in series. Plus, in parallel, you can charge as many or as few as you like and still complete the circuit. Make sure that the positive wire that connects the positive ends of the battery cases connects to the positive power post on the solar array. The same goes for the ground.

Step 4: CHARGE!

Now you’re ready to charge! Get your NiMH cells and put them into the battery cases. If you sired the cases right, they should all be oriented the same way, NOT the positive/negative way you see in most devices. If everything works, you should be able to set the solar array in the sun and charge the batteries. It would be perfect for backpacking trips if you have devices like flashlights and GPS units that run on AA batteries, and you don’t want to carry extra alkaline cells. The possibilities are limitless!




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