Many reviews on this site cover battery operated chainsaws and you will come across terms such as Lithium-ion, voltage and amp hours. In this brief article I’m going to explain some of these terms and tell you exactly what this means in terms of your chainsaw choice.
In the past, the only suitable rechargeable batteries for power tools were known as Nickel-cadmium (NiCd). As technology has developed, however, the use of this type of battery in power tools has declined for a number of reasons.
Whilst still used today, the NiCd battery has a couple of major disadvantages compared to more modern units. Firstly, they have a low energy density. I’ll explain this in more detail later but essentially it means that this type of battery is less powerful than more modern types. They usually store well but can often self-discharge, which means that they have to be recharged again before use.
The second major issue with NiCd batteries is that they contain toxic, non-recyclable metals which are environmentally unfriendly. Many countries are now restricting their use and finding places to recycle them is becoming more difficult.
Today’s chainsaws, in common with most modern power tools, use rechargeable Lithium-Ion batteries. In addition to being the lightest of all metals, lithium provides the largest energy density for its weight (around twice that of the standard NiCd unit). As such there is potential for higher energy densities and therefore greater power. Some of the benefits of Lithium-Ion units include:
• High energy density. This is a measure of how much energy a battery can hold. The more energy it can hold translates into a longer run time and typically the Lithium-Ion can hold three times more energy than its NiCd counterpart.
• Self-discharge. The rate at which a Lithium-Ion unit discharges is much lower than in other types. As a chainsaw user, this means that you may not need to fully recharge the battery after it has not been used for a short while.
• Low maintenance. Unlike other types of battery, the Lithium-Ion doesn’t require any maintenance to ensure performance.
• No memory effect. When some batteries are recharged after only being partly discharged, they seem to ‘remember’ the smaller capacity gradually reducing the amount of charge they are able to hold. Lithium-Ion units don’t suffer any memory effect meaning that they can be recharged at any time.
• Variety. There are a number of Lithium-Ion cells available for use in various modern day appliances. The batteries found in chainsaws are able to provide high current levels, which makes them ideal.
Although there are many advantages, Lithium-Ion technology is not without some disadvantages.
• Ageing. The Lithium-Ion has a finite life, the length of which depends not only on how old the unit is but also the number of charge discharge cycles it has gone through. Storing batteries with some charge (40%-50%) in a cool place will help extend their life.
• Protection required. The batteries require in-built protection to prevent them being charged or discharged too far. Fortunately, modern technology enables this to be integrated into the battery but this does add to the cost. Which leads us on to…
• Cost. This is a major disadvantage and they typically cost around 40% more than their NiCd equivalents.
You may have read that Lithium-ion batteries are unsafe and indeed seen reports of laptops and mobile phones catching fire. You should note that heat related failures are extremely rare unless there is an inherent design fault (the Samsung Galaxy Note 7 recall springs to mind). Lithium-Ion units used in power tools have a number of in-built safety features which makes them very safe to use.
What does voltage mean?
If you are considering a battery powered chainsaw, you will come across terms such as 40 volt and 80 volt. So what is voltage? A technical explanation would be that it is the pressure from an electrical circuit’s power source that pushes current through a current loop. Think about it in terms of the flow of water. If the amps are the rate of flow, the voltage is a bit like the water pressure. A higher pressure will push more water and this is the same with batteries. A higher voltage will be able to push more electrons for a given resistance, meaning a greater capacity for work and therefore more power. Battery life can also be extended, as a higher voltage unit means less current to do the same amount of work.
Amp hours – what does this mean?
You will also see reference to AH, which means Amp hours. Amps (short for ampere) measure electric current and, as described above, can be considered in the same way as the rate of water flow.
In terms of amp hours, a product which specifies say 2AH is capable of delivering a load of 2 amps for 1 hour, 1 amp for 2 hours, 4 amps for half an hour and so on. So if you have a 2AH battery in the saw and you are continuously drawing 1 amp of current, the cell will be completely depleted in 2 hours. In theory a 4AH product should be able to run for twice as long although this is not always the case. Occasionally it might deliver slightly less or slightly more than double runtime depending on how the battery has been designed.
What this means in reality
As far as chainsaws go, what exactly does this mean? Well the greater the AHs, the longer the battery will last before requiring a recharge. In terms of voltage, the higher the volts, generally the greater power the battery will be able to generate. An 80v 4AH battery would therefore be more powerful and last longer than a 40v 2AH unit. This greater performance is, however, offset by the cost and you could pay up to $200 more for high spec version. Also the larger battery is likely to be heavier and will also take longer to charge.
When using a battery powered saw you should always ensure you have enough ‘fuel’ for the task to be undertaken so it’s important that you are aware of the battery’s capabilities. If you are embarking on a large project consider taking a back-up just in case. After all, leaving a half-felled tree isn’t recommended!
Charging and storing
When it comes to battery charging and storage, you should always follow the manufacturer’s instructions.
Modern batteries can take as little as an hour right up to five hours to fully charge. It all depends on the battery and the charger being used.
In terms of storage, generally they should be kept in a cool dry place. Each battery will be different, but they will benefit from being stored partly charged. Some manufacturers recommend that if not used for a while the unit should be charged every couple of months.
I hope you have found this article useful. If you think a battery powered saw is right for you, feel free to head over to our review section and check out some of the latest models. The “Compare chainsaws” table can be used to see all the saws reviewed to date and how they compare.