BU-808: How to Prolong Lithium-based Batteries
Battery research is focusing on lithium chemistries so much that one could imagine that the battery future lies solely in lithium. There are good reasons to be optimistic as lithium-ion is, in many ways, superior to other chemistries. Applications are growing and are encroaching into markets that previously were solidly held by lead acid, such as standby and load leveling. Many satellites are also powered by Li-ion.
Lithium-ion has not yet fully matured and is still improving. Notable advancements have been made in longevity and safety while the capacity is increasing incrementally. Today, Li-ion meets the expectations of most consumer devices but applications for the EV need further development before this power source will become the accepted norm.
As battery care-giver, you have choices in how to prolong battery life. Each battery system has unique needs in terms of charging speed, depth of discharge, loading and exposure to adverse temperature. Check what causes capacity loss, how does rising internal resistance affect performance, what does elevated self-discharge do and how low can a battery be discharged? You may also be interested in the fundamentals of battery testing.
What Causes Lithium-ion to Age?
The lithium-ion battery works on ion movement between the positive and negative electrodes. In theory such a mechanism should work forever, but cycling, elevated temperature and aging decrease the performance over time. Manufacturers take a conservative approach and specify the life of Li-ion in most consumer products as being between 300 and 500 discharge/charge cycles.
Evaluating battery life on counting cycles is not conclusive because a discharge may vary in depth and there are no clearly defined standards of what constitutes a cycle(See BU-501: Basics About Discharging). In lieu of cycle count, some device manufacturers suggest battery replacement on a date stamp, but this method does not take usage into account. A battery may fail within the allotted time due to heavy use or unfavorable temperature conditions; however, most packs last considerably longer than what the stamp indicates.
The performance of a battery is measured in capacity, a leading health indicator. Internal resistance and self-discharge also play roles, but these are less significant in predicting the end of battery life with modern Li-ion.
Figure 1 illustrates the capacity drop of 11 Li-polymer batteries that have been cycled at a Cadex laboratory. The 1,500mAh pouch cells for mobile phones were first charged at a current of 1,500mA (1C) to 4.20V/cell and then allowed to saturate to 0.05C (75mA) as part of the full charge saturation. The batteries were then discharged at 1,500mA to 3.0V/cell, and the cycle was repeated. The expected capacity loss of Li-ion batteries was uniform over the delivered 250 cycles and the batteries performed as expected.
Eleven new Li-ion were tested on a Cadex C7400 battery analyzer. All packs started at a capacity of 88–94% and decreased to 73–84% after 250 full discharge cycles. The 1500mAh pouch packs are used in mobile phones.
Although a battery should deliver 100 percent capacity during the first year of service, it is common to see lower than specified capacities, and shelf life may contribute to this loss. In addition, manufacturers tend to overrate their batteries, knowing that very few users will do spot-checks and complain if low. Not having to match single cells in mobile phones and tablets, as is required in multi-cell packs, opens the floodgates for a much broader performance acceptance. Cells with lower capacities may slip through cracks without the consumer knowing.
Similar to a mechanical device that wears out faster with heavy use, the depth of discharge (DoD) determines the cycle count of the battery. The smaller the discharge (low DoD), the longer the battery will last. If at all possible, avoid full discharges and charge the battery more often between uses. Partial discharge on Li-ion is fine. There is no memory and the battery does not need periodic full discharge cycles to prolong life. The exception may be a periodic calibration of the fuel gauge on a Smart battery or intelligent device(See BU-603: How to Calibrate a “Smart” Battery)
The following tables indicate stress related capacity losses on cobalt-based lithium-ion. The voltages of lithium iron phosphate and lithium titanate are lower and do not apply to the voltage references given.
Table 2 estimates the number of discharge/charge cycles Li-ion can deliver at various DoD levels before the battery capacity drops to 70 percent. DoD constitutes a full charge followed by a discharge to the indicated state-of-charge (SoC) level in the table.
100% DoD is a full cycle; 10% is very brief. Cycling in mid-state-of-charge would have best longevity.
Lithium-ion suffers from stress when exposed to heat, so does keeping a cell at a high charge voltage. A battery dwelling above 30°C (86°F) is considered elevated temperature and for most Li-ion a voltage above 4.10V/cell is deemed as high voltage. Exposing the battery to high temperature and dwelling in a full state-of-charge for an extended time can be more stressful than cycling. Table 3 demonstrates capacity loss as a function of temperature and SoC.
What Can the User Do?
Environmental conditions, not cycling alone, govern the longevity of lithium-ion batteries. The worst situation is keeping a fully charged battery at elevated temperatures. Battery packs do not die suddenly, but the runtime gradually shortens as the capacity fades.
Lower charge voltages prolong battery life and electric vehicles and satellites take advantage of this. Similar provisions could also be made for consumer devices, but these are seldom offered; planned obsolescence takes care of this.
A laptop battery could be prolonged by lowering the charge voltage when connected to the AC grid. To make this feature user-friendly, a device should feature a “Long Life” mode that keeps the battery at 4.05V/cell and offers a SoC of about 80 percent. One hour before traveling, the user requests the “Full Capacity” mode to bring the charge to 4.20V/cell.
The question is asked, “Should I disconnect my laptop from the power grid when not in use?” Under normal circumstances this should not be necessary because charging stops when the Li-ion battery is full. A topping charge is only applied when the battery voltage drops to a certain level. Most users do not remove the AC power, and this practice is safe.
Modern laptops run cooler than older models and reported fires are fewer. Always keep the airflow unobstructed when running electric devices with air-cooling on a bed or pillow. A cool laptop extends battery life and safeguards the internal components. Energy Cells, which most consumer products have, should be charged at 1C or less. Avoid so-called ultra-fast chargers that claim to fully charge Li-ion in less than one hour.
References
[1] Courtesy of Cadex [2] Source: Choi et al. (2002) [3] B. Xu, A. Oudalov, A. Ulbig, G. Andersson and D. Kirschen, Modeling of Lithium-Ion Battery Degradation for Cell Life Assessment, June 2016. [Online]. Available: https://www.researchgate.net/publication/303890624_Modeling_of_Lithium-Ion_Battery_Degradation_for_Cell_Life_Assessment. [4] Source: Technische Universität München (TUM) [5] With permission to use. Interpolation/extrapolation by OriginLab.
The material on Battery University is based on the indispensable new 4th edition of Batteries in a Portable World. A Handbook on Rechargeable Batteries for Non-Engineers which is available for order through Amazon.com.
Best Quiet
RYOBI 550 CFM 40-Volt Lithium-Ion Brushless Cordless Whisper Series Jet Fan Leaf Blower
We love how quietly the Ryobi 40V Brushless 125 MPH 550 CFM Cordless Battery Whisper Series Jet Fan Blower with 4.0 Ah Battery and Charger operates. While its product description says it has a noise rating of 59 dB, our personal measurement with a decibel meter showed its noise rating to be 40.2 dB. We also confirmed the same decibel rating while testing in one of our homes. We also found it to be just as powerful as some gas models.
Despite its quiet operation, the unit offers a good amount of power in the form of a 550 CFM airflow capacity and a 125 mph airflow speed. In our lab tests, the Ryobi cleared a patch of grass from dry leaves in 27 seconds and from damp leaves in 28 seconds. It was significantly quicker at clearing the patch of concrete from dry leaves, finishing the job in just 11 seconds.
We also found the machine easy to start up, with the single press of a button. We did have some discrepancies in maneuverability, with our lab results describing the blower as easy to heft, while in a real-world scenario, we found this blower difficult to manage. When my husband uses it, he doesn’t quickly notice any fatigue or issues with its weight, our at-home testing team member said. He is a bigger, stronger guy. When I carry it, it does seem heavy to me, and the weight of the battery makes me tire faster. This may not be a great choice for smaller people.
The battery was another issue for our at-home testing team member, saying she got only 15 minutes from a charge. Anyone using this should definitely invest in at least one more battery, she said. She also found the chute somewhat long, which she said made it sometimes not very maneuverable in tight corners. These discrepancies could be due to our team member’s height, but we still find them to be valuable Комментарии и мнения владельцев for any shorter users searching for a leaf blower. Again, those downsides don’t keep us from recommending this as an affordable, quiet solution to keep your yard tidy when the leaves fall.
How It Performed Long-Term
Although we had some usability issues since our at-home testing team member was shorter, we still appreciate this blower’s overall design and powerful motor after several months of regular use. The Turbo Mode is especially handy for cleaning off big piles of leaves as well.
Price at time of publish: 199
Maximum Air Speed: 125 mph | Maximum Air Volume: 550 CFM | Weight: 9.7 pounds | Motor Type: Brushless | Noise Rating: 59 dB
Best Variable-Speed
WORX WG584 40V Turbine Cordless Leaf Blower Power Share with Brushless Motor
The WORX 40V Turbine Cordless Leaf Blower Power Share with Brushless Motor lets you choose from an airflow capacity of 300 to 470 CFM and from an airflow speed of 60, 69, 80, or 95 mph. We appreciated that the unit was so lightweight and surprisingly quiet for the amount of power it had. It cleared the patch of grass with dry leaves in 12.9 seconds, which was the fastest clocked time among all the other models on this list for that specific test. It cleared the patch of grass with damp leaves in 52 seconds and the patch of concrete with dry leaves in a considerably faster 12.7 seconds.
This unit is made up of three pieces. While we had no issue following the assembly instructions and finished setting the leaf blower up in less than two minutes, we struggled a bit when attaching the final piece. We wish this unit allowed us to have better control over the airflow, since we were unable to round up the leaves in the box we drew with chalk on a concrete sidewalk. However, we were pleased with its power, as it easily pushed each trimmer line a 10-foot distance. We were also pleased with its long battery life, and we never noticed a decline in power during use.
How It Performed Long-Term
After six months of regular use, we think this leaf blower is a great, inexpensive tool. While it may not be the best for precise jobs, it’s variable speed and lightweight design make it an effective and comfortable option for quickly clearing your yard of leaves.
Price at time of publish: 220
Maximum Air Speed: 95 mph | Maximum Air Volume: 470 CFM | Weight: 7.3 pounds | Motor Type: Brushless | Noise Rating: 102.1 dB
Best Backpack
Greenworks Pro 80V Cordless Backpack Leaf Blower
We initially had some hesitancies about the efficacy and overall comfort of backpack blowers, but this model from Greenworks completely dispelled any doubts. This backpack blower is comfortable to wear, easy to use, and expedites the leaf-clearing process. This model also was quieter than some other backpack leaf blowers we tested. It has a trigger-activated variable-speed throttle and a cruise control option that provides constant airflow as needed. We especially appreciated the multiple power options during lab testing, since the trigger offers more precise airflow, but the turbo mode and cruise control have a lot of power behind them.
Greenworks estimates that the fully charged 2.5Ah battery lasts only around 18 minutes if run continuously at its highest speed. We noted it ran far longer during our at-home testing because we were able to blow an entire backyard multiple times before recharging. This blower also has a charger that quickly restores power to the battery in just 45 minutes.
Despite its variable speed, this model still isn’t the most powerful of those we tested—its maximum air speed is 145 mph, and maximum airflow is 580—but it works well in smaller yards. However, we loved using this backpack blower and think it’s a great alternative to traditional leaf blower models.
How It Performed Long-Term
While a backpack blower may not be best for every yard, we think this backpack blower is a great compromise for homeowners with smaller yards. This was the easiest year of picking up leaves I’ve ever had! our at-home testing team member said. We enjoyed using this blower to not only clear leaves but also blow debris off a back deck and front porch.
Price at time of publish: 350
Maximum Air Speed: 180 mph | Maximum Air Volume: 610 CFM | Weight: 14.64 pounds | Motor Type: Brushless | Noise Rating: 87 dB
Best Gas
Echo 2-Stroke Cycle Handheld Leaf Blower
The Echo Gas 2-Stroke Cycle Leaf Blower manages to be a powerful gas model—with an airflow capacity of up to 453 CFM and an airflow speed of up to 170 mph—without being too loud, too unwieldy, or too high maintenance. We’d like to note that we have not had a chance to test this blower in our lab or at home, so our assessment is based on research alone. This model has a 70 dB noise rating, an 8.6-pound weight, and, according to users, manageable maintenance and cleaning requirements. Since this is a gas model, regular maintenance is required to keep it functioning properly, which is something to consider before purchasing it. Also note that a shoulder harness is not included with this leaf blower, though the unit does have shoulder harness points, so you have the option of buying a harness separately and attaching it to the leaf blower.
The unit relies on a recoil start (so you need to pull a cord to start operating it), but users say it’s a quick, easy, and fairly smooth start-up process. Further contributing to its user-friendliness is a translucent tank that allows you to easily monitor your fuel levels as you operate the unit, as well as an air filter that’s made to help keep the engine clean. It has a curved tube as well, which is designed to mitigate strain placed on your arms and wrist and thus help prevent them from quickly growing weary. There’s also a cruise control mode, which can help further minimize the taxing nature of your yard work.
Price at time of publish: 249
Maximum Air Speed: 125 mph | Maximum Air Volume: 450 CFM | Weight: 6.7 pounds | Motor Type: Brushless | Noise Rating: 66 dB
FAQs
Those who are still unsure about how to use a battery string trimmer may find the following answers to common questions about these tools helpful.
Q. Can a string trimmer cut weeds?
A string trimmer is used to cut and control weed growth around the home and garden. However, light-duty trimmers may have issues with very dense weed growth.
Q. Can you use a string trimmer to cut grass?
A string trimmer can be used to cut grass, though you need to be careful not to cut the grass too short while trying to keep the trimmer balanced. It isn’t the easiest way to cut the grass, but it is possible.
Q. Can you edge with a string trimmer?
Yes, a string trimmer can be used for edging the garden, driveway, walkway, or sidewalk. If you have a large yard, it may be better to invest in a separate edging tool.
Q. How many volts should be in a trimmer?
String trimmer batteries average from 18 volts up to 80 volts. Typically, the higher the voltage, the longer the battery life.
Q. How do you edge a lawn with a string trimmer?
Hold the string trimmer perpendicular to the lawn to keep the cut even. Position the head about 4 inches off the soil so the string has space to rotate. The string should rotate and cut through the grass and dirt. As you move along the desired borders, keep the head balanced and even. Clean up the cut grass and dirt to finish the job.
Why Trust Bob Vila
Bob Vila has been America’s Handyman since 1979. As the host of beloved and groundbreaking TV series including “This Old House” and “Bob Vila’s Home Again,” he popularized and became synonymous with “do-it-yourself” home improvement.
Over the course of his decades-long career, Bob Vila has helped millions of people build, renovate, repair, and live better each day—a tradition that continues today with expert yet accessible home advice. The Bob Vila team distills need-to-know information into project tutorials, maintenance guides, tool 101s, and more. These home and garden experts then thoroughly research, vet, and recommend products that support homeowners, renters, DIYers, and professionals in their to-do lists.
Meet the Tester
Mark Wolfe is a writer and product tester with a background in the nursery and landscaping industry. For more than 20 years he mowed, edged, planted, pruned, cultivated, irrigated, and renovated beautiful landscapes. Now he tests and writes reviews about the latest outdoor power equipment, hand tools, lawn-care products, and other outdoor-living goods.
Additional research provided by Glenda Taylor.