lithium ion battery FAQs Power Tools

Lithium Ion (Li-ion) Batteries – FAQs

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.

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 is the difference between 20V and 40V batteries? Is bigger better?

On the one hand, 40V battery cordless operated tools have more power than 20V batteries and their batteries usually last longer. On the other hand, 20V battery tools are lighter and smaller, as well as cheaper to buy.

40V batteries are ideal for users who use the tool often and for longer periods of time. The cheaper 20V batteries are a better investment if the battery operated tool is used only seasonally or rarely.

Although larger voltage batteries are being seen on the market, such as a 120V battery for the new Redback lawnmowers that will be introduced soon, they are specific to their brand and not for use in other manufacturers’ tools.

Some newer batteries are also being designed to automatically change voltage to suit the power requirement of the tool, such as the FlexVolt battery from DeWalt. It should be noted that the flexibility comes with a large weight difference, averaging about a pound heavier than a 20V battery.

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).

Obviously, 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.

So a 4.0Ah battery pack lasts 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 battery packs are designed.

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 new 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. Good news is, 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 charge 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 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, a lithium-ion battery with a very low charge is stored for a long period of time (many months) and its voltage slowly drops to below the level at which its built in safety mechanism allows it to be charged again.

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 it 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.

If I have a 20V tool, can I use a 40V battery?

Sometimes.  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.

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!

4 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.

  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).

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