Is it dangerous to charge a hedgetrimmer battery for too long?

How modern lithium-ion batteries work

/ Inspirations

13/09/2023

Estimated reading time 5 minutes

Lithium batteries, or strictly speaking lithium-ion batteries, are at the heart of many of the electrically powered devices we use every day: from mobile phones, drills and laptops to gardening tools, bicycles and cars. Our work, free time, communication and mobility literally depend on lithium-ion batteries, which are the most efficient type of battery currently available.

As far as we are concerned, there are several good reasons for preferring battery-powered gardening tools: they are quiet running, they don’t emit exhaust fumes, you can turn them on simply by pressing a switch, you don't need to buy fuel to top them up with, and you don't have the constraints of cables and power sockets.

How does a lithium-ion battery work? How long does it last? Do I have to follow any safety rules when using and recharging it? Is there a knack to making it last longer? These are some of the questions we will answer in this article. For convenience we will focus on hedgetrimmer batteries, but the same advice applies to all battery-powered gardening tools.

How does a lithium-ion battery work and how long does it last?

Lithium-ion batteries are also called accumulators because during charging, they store current which they then release in the discharge phase to battery-powered hedgetrimmers, for example. What makes these rechargeable batteries work? The reversible chemical reactions of lithium ions. Lithium is a light solid metal that easily gives up its electrons (thus providing electrical energy), which move from one electrode to another in the battery during the charging and discharging phases.

A special feature of lithium-ion batteries is that they contain a lot of energy in a small space and have low weight. Battery packs are made up of lithium-ion cells. Irrespective of their shape or size, each cell consists of a pair of electrodes (one positive and the other negative, respectively the cathode and anode) isolated by a separator and moistened with electrolyte. The latter is a liquid that conducts electric current thanks to the lithium ions, thereby recharging the battery.

The capacity of a lithium-ion (or Li-ion) battery is measured in ampere-hours (Ah) and indicates the amount of current that it can supply in one hour. But how long does a lithium-ion battery last? Battery life depends on the battery’s capacity, the type of machine being operated (a hedgetrimmer in our case), the workload (demanding or light, basically how much current the hedgetrimmer draws). Generally speaking, the higher the capacity, the longer the battery life: we test it in this article about how much you can get done in the garden on one battery.

If you don't yet have a battery-powered hedgetrimmer, here is a summary of the advantages of battery-powered gardening tools and a comparison between different types of hedgetrimmers (battery, electric and petrol engine).

Is it risky to leave a lithium-ion battery charging unattended?

To ensure optimal performance, recharge lithium-ion batteries often, rather than waiting until they are completely discharged. Furthermore, exhausting a lithium-ion battery completely makes it age faster:

  • Ensure that the mains voltage is compatible with the charger.

  • Place the charger on a surface that allows heat to escape (not on top of a blanket, for example).

  • Keep its ventilation grilles clean and unblocked.

Lithium-ion batteries are manufactured to high safety standards, but they must be treated with care. They store concentrated energy, which if released in an uncontrolled way due to electrical overload, overheating or mechanical damage (impacts, dropping, etc.), could cause the battery to catch fire, explode or release toxic gases.

What happens if you leave a lithium-ion battery charging in your hedgetrimmer (or other gardening tool) for longer than it should? Does overcharging heat up the battery and cause it to catch fire? No, nowadays the risk of overload and overheating is minimal: modern lithium-ion batteries are equipped with an electronic internal management system that communicates with the battery charger. For example, in the event of overload and overheating, the LED indicator light on Oleo-Mac battery chargers slowly flashes red and charging stops. If this happens, unplug the charger, disconnect the battery and, if you still need to charge it, wait for it to cool.

When charging is finished–when the LED light is solid green–don’t leave the battery inserted in the charger, and unplug the battery charger from the power socket.

The same internal management system also monitors the battery for overheating during operation: if it detects an anomalous temperature, it causes the hedgetrimmer to turn off (this may happen in the event of intensive use). For these reasons, it is important that the hedgetrimmer is only fitted with an original lithium-ion battery made by the same manufacturer, and that this battery is charged using a compatible battery charger.

Heat is the worst enemy of lithium-ion batteries for a variety of reasons including safety, efficiency, battery life and duration. Therefore:

  • Store them in a cool place (for example, the ideal temperature for Oleo-Mac batteries is 15°C).

  • Never leave them exposed to the sun, inside the boot of a car in summer, or near to heat sources (such as radiators).

  • Only charge them in an ambient temperature between 10 and 40°C (just like hot weather, cold temperatures are not good for lithium-ion batteries).

A battery that has suffered damage from overheating or cold must be replaced. It should also be replaced if cracked or broken due to being dropped or struck against something. Has it been dropped but the outer casing seems intact? The lithium-ion cells may nevertheless have been damaged. If you have any questions about Oleo-Mac batteries, contact your nearest service centre.

Storage of lithium-ion batteries and battery-powered tools

At the end of the season, what is the best way to store a lithium-ion battery for a hedgetrimmer or other battery-powered gardening tool? It depends on the characteristics of the battery itself, which may need to be maintained at a certain temperature and a precise charge level. You can find all the instructions in your user manual: we recommend you read it so that you can keep the battery and charger safe at all times.

Here is a recap of the instructions for storing Oleo-Mac lithium-ion batteries:

  • Remove the battery from the hedgetrimmer (or brushcutter, lawnmower, chainsaw or blower).

  • Recharge it to 100%.

  • Put it back in its packaging, so that it is protected from impact, and place it in a dry environment, away from rain, moisture and cold.

  • Don’t keep it in the sun, in warm environments or near to a heat source, but do keep it at a temperature of between 10 and 20°C.

  • Keep metal objects (nails, coins, etc.) away, as they can cause a short circuit.

  • Maintain a minimum charge level of 40%: even if it’s not being used, the battery slowly discharges by itself, so check it and charge it every month or so.

It’s not just the battery that needs careful maintenance: here is an overview on hedgetrimmer maintenance to help you prune your plants to perfection.

Are you excited about the results of your battery-powered hedgetrimmer and thinking of purchasing a lawnmower with the same type of power source? Here you will find an article comparing different types of lawnmowers.

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