September 17th, 2018 by
If you’re a DIY enthusiast (or simply the one who gets put-upon to fix things around the house!) you’re probably familiar with power tools. As you’re looking around drills, hedge-trimmers, multi-tools, and the rest, you’ll probably see that different types of power tools have different types of battery. There are three main types of battery that you’ll come across; Nickel-Cadmium (Ni-Cad), Nickel Metal Hydroxide (Ni-MH), and Lithium-Ion (Li-Ion). So, what’s the difference between these battery types and which one is best for you? Read on for a complete guide to power tool batteries!
What to Look Out for When Buying Power Tools
The battery is arguably the most important part of any power tool – if the battery isn’t good enough, your power tool will be useless! If you’re not a professional tradesman, though, you might not know what to look out for when you’re looking at a power tool battery. We’ll outline a few of the key terms below, then round up which battery is best in which area.
Are Ni-Cad Batteries Legal?
Ni-Cad batteries were banned by the EU thanks to the environmental damage caused by the cadmium they use. This means you can no longer buy new power tools that use Ni-Cad batteries, although you can still buy replacement Ni-Cad batteries for your existing power tools. Shops are also still allowed to sell old Ni-Cad stock that was manufactured before the ban came into force (on 31st December 2016), so you’ll likely see Ni-Cad drills for sale at knock-down prices. This could be a false economy, though – the batteries are likely old and won’t offer the same performance or value for money that Li-Ion or Ni-MH batteries do. As you can’t buy any new power tools with Ni-Cad batteries, we won’t include them in our roundup below.
Voltage
Voltage is simply a measurement of how much power you’ll get out of your power tool. Naturally, more heavy-duty work (such as drilling metal) needs a higher voltage tool. For DIY purposes, anything around 18-20V will be powerful enough to handle most jobs. Inside a battery, there are several cells which each have their own voltage. The voltage of all these cells added up is what gives you the overall voltage that you’ll see advertised on the box of your power tool. Each type of battery has a different cell capacity, so, for example, Li-Ion battery cells give around 4V each, so you’d need around 5 to power a 20V cordless drill. However, Ni-MH battery cells only have a capacity of around 1.4V, so they need many more cells to give you 20V of power. This means you’ll need a bigger, bulkier battery! Li-Ion batteries have the best voltage per cell, delivering between 3.6-4.2V per cell so you’ll find they’re smaller. Ni-MH batteries only offer around 1.4-1.6V per cells, so you’ll find they’re much bulkier.
Capacity and Battery Life
This is a very important thing to look out for – simply put, this is how long you can use your power tool for before the battery dies and needs to be recharged. Capacity is measured by milliamp hours (mAh) – all you need to know is the higher the mAh number, the longer your battery will last! Li-Ion batteries offer the highest capacity or around 3 mAh. Ni-MH batteries can offer between 2.2 and 3 mAh so are a good cheaper option.
Charge Cycle Count
Every time your battery runs down to empty and has to be charged back up again, that’s what’s known as a charge cycle. The charge cycle count is how many times the battery can be depleted and recharged before it starts to stop holding charge. This number can vary depending on how well you treat your battery. Li-Ion batteries have a can be charged up to 500 times before they start to stop holding charge. A Ni-MH battery’s charge cycle count is hugely variable depending on how you maintain your battery (see the rest of this article for more info on this). If you look after your battery, you can get well over 1000 charges out of it. If you don’t, your battery could become useless after only a few hundred charge cycles.
Memory Effect
Some batteries have a form of ‘memory’ which means they remember what points they’re charged and discharged to. If you don’t charge your batteries properly, they can ‘remember’ where they were charged to which can reduce their battery life. This means it’s usually wise to fully discharge your battery before you start charging it back up again. Also, make sure you fully charge your battery to keep its battery life as long as possible. Some types of battery are more susceptible to the memory effect than others. Li-Ion batteries are barely affected by the memory effect, meaning you don’t have to stress about how much you’re charging them all the time. Ni-MH can suffer from the memory effect if they’re not charged and discharged properly.
Deep Discharge
Deep discharge is the process of completely running your batteries down. This can be confusing as, for some batteries, deep discharge can reduce your battery life. However, other batteries need an occasional deep discharge to stay functional! If you don’t use your power tools much, this can be an unnecessary hassle, so it’s definitely a factor to consider. Li-Ion batteries don’t need a deep discharge and shouldn’t be affected by being completely drained. However, if you deep discharge a Li-Ion battery and leave it empty for weeks at a time, this can damage the battery. Ni-MH batteries should be deep discharged once every three months or so to keep the battery healthy.
Self-Discharge
Batteries will gradually lose charge even when they’re not in use. Different types of battery have different discharge rates, so you’ll find some tools will hold their charge for much longer than others when in storage. Li-Ion batteries barely lose charge at all when they’re not in use – in fact unless you leave them unused for years, they won’t lose any charge at all! This makes Li-Ion tools a much better option if you only use your power tools on occasion. Ni-MH batteries have quite a fast self-discharge rate, but if you’re using your power tools regularly this shouldn’t be a problem.
Sensitivity
As you might have gathered, there’s a lot of chemistry involved when looking at batteries! Different batteries are made up of different chemicals, and some are tougher than others. A sensitive battery is more likely to be affected by heat and cold, as well as heavy impacts in some cases. Li-Ion batteries are sensitive to high temperatures, so try not to let your battery overheat and don’t leave it out in the sun on a hot day. They can also be damaged by hard impacts, so try not to drop them too much! Ni-MH batteries are sensitive to high temperatures too, but they’re more affected by the cold. Try not to leave your Ni-MH power tools outside on a freezing day!
Overall
As you can see, Li-Ion batteries are comfortably the best performing battery, easily outstripping the Ni-MH in almost every area. They’re smaller, more powerful, and don’t require much maintenance. They are a little more expensive than a Ni-MH equivalent, but it’s definitely worth the extra cost, especially if you don’t want the hassle of having to discharge your battery every few months.
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