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A buyer’s guide to power tool batteries – all you need to know about the latest battery technology


With the promise of more power, extended runtimes and longer overall battery life, the advances in power tool batteries have increased significantly in the last few years. Just as the technology has changed so have the rules regarding the ways batteries should be used and maintained.

Buying batteries now becomes an investment as prices can reach almost £70 in the 18V 4Ah range. Each battery has its own unique advantages within the 18V series, whether that’s price, performance or warranties. Still, when making the investment it’s important to be clear about what the benefits are and to be sure you’re continually getting the best from your battery. Hopefully what this guide will do is provide clarity on which is the best for your requirements.

There’s nothing wrong with my memory

Battery terminology can make things confusing and advances in Lithium-Ion technology mean that what was once applicable to older batteries is now not the case. Memory Effect or battery memory is a term that applies with older NicCd and NiMh batteries where the battery remembers the last capacity point. In essence if a battery is continually recharged after a short discharge, the maximum capacity is lost as the battery memorises the level of the last charge.

True or False – Li-Ion Batteries need to be fully discharged in order to maintain capacity?

False. While it’s true that NiCd and NiMh batteries needed to be fully discharged to keep their optimum condition, the opposite is true for Lithium-Ion batteries which should NOT be left to fully discharge as this can actually damage the battery. Li-Ion also doesn’t suffer from Memory Effect and so can be charged at any point.

As soon as the performance of the battery has started to decrease and you can start to feel a loss of power, get the battery on charge. It doesn’t matter if the battery isn’t fully topped up before using it again, as long as some extra charge has been put in. It’s ok to part charge these.

Never let the battery run all the way down, for example if you’ve got one last screw to turn and then the battery is depleting, don’t force it over the final furlong. You shouldn’t keep your finger on the trigger and keep turning to try and drive the screw. Let it rest and put the battery on charge. Forcing it is a definite way to damage the battery. You can always top it up briefly and then come back to finish.

Who has absolute power?

Each manufacturer’s batteries have their own distinct advantages. It’s up to you to decide which best suits your needs.

Makita’s unique position with its 18V battery is that it has the world’s largest range of compatible cordless tools. Over 100 of Makita’s tools can be powered by their 18V Lithium-Ion battery giving you a huge selection to work with. They also have some of the fastest charging times with a 3Ah battery taking 22 minutes, 4Ah ready in 36 minutes and the 5Ah complete in just 45 minutes.

By comparison, Bosch has some of the smallest and lightest batteries on the market and this can make a real difference especially when doing a lot of overhead work. They also have a robust construction, having been tested to withstand being dropped from 3 metres. Inside, each battery is fitted with Electronic Cell Protection (ECP) which protects the battery against total discharge, overloading and overheating. See the results of their heat test here.

Festool’s 5.2Ah battery again is equipped with leading battery technology and the company highlights the cell balancing that goes into its units. This involves carefully selecting equally matched cells, resulting in proportionate charging and discharging cycles which prolong battery life. Interestingly, Festool are so confident in the quality of their batteries that their 3 year service all-inclusive guarantee also covers batteries and chargers.


Axminster’s battery for the Makita 18V Li-Ion cordless tools, however, is fitted with Samsung SDI cells. Analysing the battery cell market, Samsung SDI is the market leader in small size rechargeable batteries producing 315 million cells a year, so they know what they’re talking about when it comes to batteries. There are many cheaper replica batteries out there using inferior quality cells and that’s when you have problems with the batteries failing after a few cycles.

A look to the future

Bosch have developed a world first with their wireless charging system which is able to charge the battery without having to take it out of the tool as with the GSB 18V Combi Drill. If time is of the essence, as it invariably is, this is perfect in repetitive situations where you need to pick up and put down the tool over long periods, as the battery is continually topped up without interrupting your work.


With all these advances to battery power, there is now some interesting technology that can utilise this power, not only for your tools but also your mobile device.


Over time the power of batteries is surely set to increase with higher ampere-hour (Ah) and longer runtimes. If you look after your batteries, this will help to prolong their life to give you even greater value for money. Here we go into greater detail about the optimum conditions for maintaining batteries and some further specifications to help you differentiate between manufacturers.

How to store your batteries

Make sure batteries aren’t subjected to extremes of heat. Ideally they should be kept at room temperature as heat is one of the main reasons Li-Ion battery life will be depleted. So avoid leaving power tools in the car or van if it’s going to be out in the sun for a long time. Equally freezing conditions can reduce the lifespan of the battery – something to remember on those long winter nights.


Obviously when the batteries are used continuously over extended periods, this can cause the core of the battery to heat up considerably. This is something that the people in white coats at Bosch have counteracted with their CoolPack technology. Similar in refrigerator functionality, the casing conducts heat so it can dissipate away from the core cells, enabling longer runtime and battery life.

Discharge rates have improved with Lithium-Ion technology, meaning that when batteries are not in use, the charge is held within the battery for longer. If you’re not going to be using your power tool for an extended period however, ensure there is some charge in the battery. Leaving a fully discharged battery for a long time is one of the quickest ways to cause it to fail.


As batteries have evolved and tools are updated, using the wrong type of battery can cause problems if placed in the wrong tool. You want to make sure you’re using the right battery for the tool and each manufacturer has its own way of identifying the correct compatibility.

With Bosch, quite simply if the battery doesn’t fit in the tool then it’s not the right battery. The Bosch batteries are specifically designed so the corresponding batteries will slot into the corresponding tool. Similarly only relevant (4Ah/18V) batteries will fit in the relevant charger.

Makita’s compatibility checker works on the principle that if it has a star or a yellow connector then you’re good to go. The 18V 4.0Ah and 5Ah (BL1840 / BL1850) batteries will work with your 18V tool if it has any of these three characteristics:

1. A star on the connector plate
2. A star on a yellow connector plate
3. Or just a yellow connector plate


Festool standardised their batteries a while ago which means if you’re buying into Festool the battery can be used again in other tools across the range. Except for the new CWS compact drill, current Festool cordless drills will work with batteries made since 2005. The batteries also feature a built-in LED light which lets you know when it’s time to swap them over.


Axminster – 1 year
Bosch – 2 years
Festool – 3 years
Makita – 1 year

Festool’s service all-inclusive guarantee also applies to its batteries and chargers. Remember this covers repair costs as well as theft for up to 36 months. But to ensure you’re covered you need to register.


When it comes to weight, it might not seem like much but the additional weight of the battery can make a difference especially when using your power tool for extended periods. Here we have a weigh-in showing who the heavyweights and lightweights are…

  • Richard Wilson

    Really good article – Helpful and informative =) Good stuff chaps!

  • Adrian Manning

    Hi , i would be a great selling point ,to have a video shots, to the products you are selling , and how to use them , i think it would increase sales , thanks

  • Stamford Stoddard

    Does it harm the batteries if put on charge overnight or longer if left in the charger with the power on?

  • Jacqueline Hunt

    Hi Stamford – firstly, apologies for the delay in getting back to you. All manufacturers say that leaving the battery on overnight will be ok, but batteries should not be left on charge for days on end. For instance, Makita state the following about their batteries: “Makita chargers are designed so that they will not overcharge a Lithium-Ion battery. As an example, the DC18RC communicates with slide-type Lithium-Ion batteries to detect its charge level. Upon reaching a full charge, the charger goes into maintenance mode and actively monitors the battery’s charge level to keep it fully charged.”

  • Bob Barfield

    I have my charging post on a plug timer which I set for, well depending on the battery to be charged, I can then leave and forget