lithium ion battery FAQs Power Tools

Lithium Ion (Li-ion) Batteries – FAQs

Updated May 25, 2019

As battery-powered yard and garden tools become more common, questions always come up about the batteries. So we’ve provided answers to the most frequently asked questions from our readers. Let us know if there’s anything else you’d like us to cover in these FAQs.

If you’re looking for where to buy specific batteries for common outdoor power equipment brands, scroll to the end of this article for details.

What is the difference between Lithium batteries and Lithium Ion batteries?

There are several important differences. The practical difference between Lithium batteries and Lithium-ion (Li-ion) batteries is that most Lithium batteries are not rechargeable but Li-ion batteries are.  From a chemical standpoint, Lithium batteries use lithium in its pure metallic form.  Li-ion batteries use lithium compounds which are much more stable than the elemental lithium used in lithium batteries.

A lithium battery should never be recharged, while lithium-ion batteries are designed to be recharged hundreds of times.

What does voltage mean in batteries (e.g., 40V, 120V)? Are more volts better?

Volts are a measure of voltage and refer to the size of the force that sends electrons through the battery’s circuits. It’s sort of like horsepower, except for cordless tools. More volts equal more power available for the tool to use.

Cordless tools that use a higher voltage battery will have more power than those with lower voltage batteries. The question to ask yourself is whether or not you need that amount of power for what you’ll be doing with the tool. For example, if you’ll only be using your cordless string trimmer to trim grass around flower beds, you don’t need 120V (you can practically cut down a tree with some of the new 120V trimmers!).

On the other hand, lower voltage batteries are lighter and smaller, as well as cheaper to buy.

Higher voltage batteries are ideal for users who use the tool often, for longer periods of time and under tougher conditions. They’re also often needed in tools that require more torque or power, such as cordless chainsaws and self-propelled lawnmowers.

The cheaper, lower-voltage batteries are a better investment if the battery operated tool is used only seasonally or rarely, is used for light-duty tasks, or if weight is a consideration.

Some batteries, such as the FlexVolt battery from DeWalt, are designed to automatically change voltage to suit the power requirement of the tool.

different sizes of li-ion batteries

Li-ion batteries come in a wide range of shapes and sizes, depending on the manufacturer, volts and Ah.

What does Ah mean? How does it affect power and/or run time?

Ah is an abbreviation for ampere-hour, or amp-hour. This is the total amount of charge a battery can deliver in one hour. A power tool that continuously draws 1.0A of current will completely drain a 1.0 Ah battery pack in one hour (under ideal conditions).

This means that a 2.0Ah battery pack can power the same tool longer than a 1.0Ah battery pack can, assuming the current flow remains at 1.0A and there are no other differences. Many people simplify this to say that a “higher Ah means longer run time”, although that’s not the whole story.

So a 4.0Ah battery pack will run your outdoor power equipment twice as long as a 2.0Ah battery pack, right? Sometimes, yes. Other times, no. And sometimes it can deliver more than double the runtime. It depends on how the batteries are designed (e.g., running battery cells in parallel vs in series, built-in safety features, venting), as well as tool design (e.g., a trimmer with high and low settings will draw more or fewer amps depending on which setting is used) and environmental factors (e.g., using the battery in high heat will reduce efficiency and run time).

Without more information about the battery, all you can say for certain is that a battery with a higher Ah rating will produce power for longer than a lower Ah battery of the same voltage when used in the same tool and under the same conditions.

If you’re considering a battery for a tool that requires a lot of power or torque to be effective, then a higher Ah battery would be a plus as you’ll get more run time from the battery. If it’s a light-duty tool, then a lower Ah battery will be just fine as it won’t need to draw as many amps to work well (with the added plus of being considerably less expensive).

Do Li-ion batteries develop a memory? Do I need to recharge after every use?

No. While older styles of battery did develop a “memory”, the current Li-ion batteries do not.

Best practice is to place the battery on the charger after each use. That way, you’ll always have a fully-charged battery to work with. Many manufacturers suggest a less than full charge to prolong the overall life of the battery.

Can I use a different brand’s batteries in my tool?

No. Tool companies like to create addicts. The good news is that it pays to become an addict. Manufacturers inspire brand loyalty by selling tools, both with batteries or without. That way, once you’ve bought your first tool – and its included batteries – you can use them on all the other tools from that manufacturer. But only on tools from that manufacturer.

It’s a good idea, then, to make your buying decision based on everything a company sells, even tools that you might not need yet.

What are the advantages of Lithium Ion batteries compared to other rechargeable batteries?

Lithium-ion batteries have several advantages:

They have a higher energy density than most other types of rechargeable batteries.  This means that for their size or weight they can store more energy than other rechargeable batteries.

They also operate at higher voltages than other rechargeable batteries.

Lithium-ion batteries also have a lower self-discharge rate than other types of rechargeable batteries.  This means that once they are charged they will retain their charge for a longer time than other types of rechargeable batteries. For example, NiMH and NiCd batteries can lose anywhere from 1-5% of their charge per day (depending on the storage temperature) even if they are not installed in a device. Lithium-ion batteries will retain most of their charge even after months of storage.

li-ion batteries in chargers

Each manufacturer has their own size and shape of charger, and even within the same brand you’ll find different chargers for different batteries (note the two green Greenworks batteries/chargers in the image above).

Can I leave Li-Ion batteries on the charger?

Unless your tool instructions specifically say to store the battery on the charger, be sure to remove it after charging is complete. Overcharging can damage a battery and shorten its life, and not all chargers shut off automatically.

How long will it take to charge?

Li-Ion batteries charge quickly, usually 60-120 minutes depending on the voltage. Check the manufacturer’s directions prior to use.

What are the disadvantages of Lithium-Ion batteries compared with other rechargeable batteries?

Lithium-ion batteries are more expensive than similar capacity NiMH or NiCd batteries. This is because they are much more complex to manufacture.  Li-ion batteries actually include special circuitry to protect the battery from damage due to overcharging or undercharging.  They are also more expensive because they are manufactured in much smaller numbers than NiMH or NiCd batteries.  Li-ion batteries are becoming less expensive and over time we should see their price decrease significantly.

Lithium-ion batteries also require sophisticated chargers that can carefully monitor the charging process.  And because of their different shapes and sizes, each type of Li-ion battery requires a charger designed to accommodate its particular size and its particular manufacturer. This means lithium ion battery chargers are more expensive and more difficult to find than NiMH and NiCd battery chargers.

Are Lithium-Ion batteries available in standard sizes like AA, C or D cell size?

No, Lithium-ion batteries are not available in standard sizes.

This could be because it would be too easy for users to inadvertently put them in a charger not designed for Lithium-ion batteries, creating a potentially dangerous situation. If an alkaline battery is put into the wrong charger it might leak or even burst, but a lithium-ion battery put into a NiCd or NiMH charger not designed for lithium-ion might ignite.

Also, because Li-ion batteries operate at a much higher voltage (typically 3.7V per cell) than the 1.2 to 1.5V of most cell batteries, designing a 1.5V lithium-ion cell would be expensive.

What is the best way to store Lithium Ion batteries?

Lithium-ion batteries can hold a charge for many months. It is best to store a lithium-ion battery with a partial or full charge.

Occasionally, if a lithium-ion battery with a very low charge is stored for a long period of time (many months) you may find that its voltage slowly drops to below the level at which its built-in safety mechanism allows it to be charged again. In other words, it’s dead.

If the battery is going to be stored for several months it’s a good idea to take it out and recharge it after a few months. Better yet would be to actually use the battery every few months and then leave it partially or fully charged.

Do I need to charge the battery when I buy it?

Most Li-Ion batteries come with a partial charge. Most manufacturers specify in their instructions how long to charge a new battery before using it for the first time. Usually, this means topping off the charge before first use.

How should I dispose of Lithium-Ion batteries?

Li-ion batteries, like all rechargeable batteries, are recyclable and should be recycled rather than thrown in the trash.  They should never be incinerated since they might explode. Most places that sell rechargeable batteries will also accept them back for recycling.

Does the battery “die” after a while?

Yes. You can expect a lithium-ion battery to last from two to three years.

A lithium-ion battery’s lifespan is calculated by charging and discharging cycles. The typical lithium-ion battery has a lifetime of up to 2000 charging and discharging cycles.

Check your individual warranty – the battery should last at least that long.

Can I use a higher voltage battery than the one that came with the tool?

Sometimes, although not a much higher voltage (e.g., do not try using a 120V battery in a tool that comes standard with a 20V battery!). As previously stated, batteries are indigenous to their manufacturers and many are now offering interchangeable voltage options. Keep in mind that higher voltage equals heavier weight and greater cost. Check your tool’s manual for specific guidelines.

redback battery sizes

Li-ion battery sizes differ so even in cases where a battery has the same volts (40V in the image above), if the Ah is different the battery size will likely also be different and so may not fit on the same tool.

Where to Buy Li-Ion Batteries

Below are some of the most common batteries for lawn and garden tools.




Sun Joe / Snow Joe


Yard Force

Please note that the Amazon links (and only the Amazon links) above are affiliate links. Should you choose to purchase products through these links, GPReview will make a small commission (at no extra cost to you) that helps to support this website and our gardening product reviews. Thank you!

12 Comments on Lithium Ion (Li-ion) Batteries – FAQs

  1. Herb

    Nova was on the other night and featured about the dangers of the Lithium-ion battery. The SunJoe lawn mower, Model iON16LM uses a 40-Volt, 4.0 Ah Lithium-ion battery. Should this lawn mower be returned to the store from where it was purchased?

    • I don’t think you have anything to worry about, Herb. The Li-ion batteries that exploded were of a different design than what’s found in a cordless lawn mower. These are much more rugged and designed to withstand the bumping and vibration of lawn mowing.

    • Monica,
      In early summer I bought a Ryobi 40v self propelled lawn mower to be used as a backup and somewhat as a novelty.
      Upon using it on trial run I quickly found the 5 ah battery was not quite adequate to mow my entire lawn on one charge. Checking with Home Depot, I found additional battery to be quite pricey so I found a 40v 6ah to order from China to be less than half the price, so I ordered 2, just in case.
      Upon trying to use these, I find they will only run mower about 50 seconds, then stop.
      After resetting, it will run about another 50 seconds, then stop again. This will happen throughout the entire charge.
      To me this just not make any sense at all!!
      Any thoughts or ideas?

      • The 6aH battery *should* work in your mower. I’m assuming that the batteries are fully charged. Do you have access to another Ryobi 40V tool that you could try the batteries in? That would help you pinpoint whether the issue is the batteries or the mower.

        The one thing that comes to mind is the possibility of a loose connection somewhere. Sometimes it can be the mower handle that isn’t tightly locked in the fully-extended position so the connector carrying power may not be in full contact. Or it could be the power cable attachment to the battery compartment. Any loose connections can lose contact when the machine starts vibrating. Take a look at those first.

        Does the battery seem to be getting hot? Most will cut out if they overheat – give them a rest and they’ll restart. But if all you’re doing is mowing for 50 seconds, the battery shouldn’t overheat – it if does, it’s most likely a faulty battery.

        My guess is that those batteries were cheap for a reason…

  2. Joseph Gregory

    I found out how cordless trimmers lack in trimming time. I have a large area to trim, and tough weeds to cut. The battery lasted less then 20 minutes. I still had 3/4 of the backyard to weed eat. I took the cordless back to Lowes and replaced it with a corded trimmer the next day.

    • Not all string trimmers are built to run for the same length of time. Many of the newer ones, especially those with 80 or 120v batteries, run for well over 60 minutes. Unfortunately, those aren’t the ones you’re likely to find at the big box stores. Check out our article on the Best Cordless String Trimmers for some of the better options (with much longer run time).

      • Karen

        Hi Monica
        We recently bought the OREGON 36V 4.0AH LI-ION BRUSHLESS CORDLESS 40CM LAWN MOWER (9940X). It’s an excellent lawnmower but the battery drains after approx 20 minutes of use, is the battery faulty or the lawnmower ?
        Hope you can help

  3. Gary Wilson

    A question about charging: I see you say a battery should last 2-3 years or 2000 charging cycles. I use a 40V lawn mower once a week from May through November, or roughly 28 times a year, recharging the two batteries which are drained each week. Wouldn’t that only count as 28 cycles/year? The two batteries are already failing after only three years’ of use. That is, I’ve gone from being able to mow my front lawn with one battery to requiring both, and the 2nd one generally fails and needs to be nursed though a few cool offs to finish the job. Is that normal?

  4. Roger Patterson

    I am curious about compatibility between the Greenworks 80v Max and the Kobalt 80v. They look exactly the same. Would the Kobalt not work or damage the Greenworks equipment?

  5. Willis Ragland, Jr.

    I have a 120 volt 300mh battery used one summer with a chain saw and a leaf blower and it now will not recharge with only the red light on a battery chack after overnight charging on two separate functioning chargers. That seems a short life to me and I really need the long life of the battery right now to blow a ton of leaves. Thanks.

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