Cordless Tool Batteries – A Primer

Posted by on December 28, 2005

Just Looking for Power Tool Batteries?

We sell them. Get to the battery you need. (I only put this here, because I noticed a lot of people were finding this article, when they were simply looking for a battery.)

The Basics

Power tool batteries are made up by taking several lower voltage cells and hooking them together in series. Each cell has the same rating in Amp hours (a measure of how much electricity flows through a circuit in one hour with a flow rate of 1 ampere). So an 18v tool might have 12 cells at rated at 1.5 volts and 2.4 Amp hours, which would produce an 2.4Ah 18 volt battery.

Almost all of the cordless tools on the market today use one of the following three battery technologies:

  • NiCad / NiCd (Nickel Cadmium) – Nickel Cadmium batteries are commonly found in tools from Dewalt, Bosch, Porter Cable, Milwaukee, Skil and Hitachi. Advantages and disadvantages of NiCad are:
    • Least expensive cell technology
    • Has the least temperature sensitivity of the three battery types
    • A large number of charge cycles is possible
    • Stored batteries quickly lose charge
    • Can develop a sort of “memory effect” (see the below section on memory) if not regularly drained and fully charged (sometimes referred to as conditioning)
    • Cadmium is a heavy metal and is considered an environmental hazard
  • NiMH (Nickel Metal Hydride) – Nickel Metal Hydride batteries are used extensively by Makita and Panasonic. The advantages and disadvantages of NiMH batteries are:
    • Much higher potential capacity than NiCad batteries
    • Requires less conditioning than NiCad
    • While you still shouldn’t just toss a NiMH battery, it is considerably less toxic than a NiCad
    • Much more sensitive to temperature than NiCad
    • Some studies show that the battery performs less reliably after repeated empty to full charges
    • Loses a charge more quickly than NiCad
    • Much higher capacity than even NiMH
    • Charge loss during storage is less than half that of NiCad
    • No memory at all, no periodic conditioning is needed
    • From the early reports we are hearing on the Makita and Milwaukee units, lithium ion seem at least as temperature sensitive as NiMH
    • The charging process is much more complicated from a technology standpoint, meaning more expensive chargers or batteries (depending on the manufacturing choices)
    • The battery manufacturing cost is substantially higher

So Why are Power Tool Batteries so Expensive?

From time to time I hear someone complain about the price of tool batteries, although thanks to a few of our power tool manufacturers coming out with battery 2-packs, I’ve been hearing less of that particular complaint. But the idea behind the complaint is that I can go out and buy a 12 pack of AA batteries for under $8. That is 12 cells x 1.5 volts, or 18 volts total.

Of course, this point of view requires you to forget that your standard alkaline batteries are not rechargeable. So if you get 400+ charge cycles out of a cordless tool battery, then that $8 18 volt battery suddenly costs you $3,200. That is not even taking into account current draw and other issues that would make a AA cell less than ideal for the purpose.

The costs in rechargeable batteries also are influenced by the makeup of the battery. NiCad, NiMH and Li-Ion are all much more expensive per cell than a lead-acid or alkaline cell. In addition, there are costs in designing the packaging, wiring the cells and otherwise making it work safely and effectively in a power tool.

Memory

Voltage depression is the technical name for what people commonly refer to as memory in Nickel-Cadmium or Nickel Metal-Hydride batteries. While NiCad and NiMH are both capable of developing voltage depression, it is less likely with power tools than with low amp draw items like laptops or cordless phones. The effect is caused when the cells in a battery are drained to the same level at the same speed frequently. To quote a Makita training pamphlet on batteries:

This does not happen with tools in industrial applications due to the fact that tools are used in various applications. For instance, sometimes a battery will be used in a high current draw application such as installing large lag screws and other times in a low current draw application such as installing deck screws. The changes in draw and the rate of discharge prevent memory from occurring.

The voltage depression is actually caused by crystalline structures forming on the nickel plate (on both NiMH and NiCad) and the Cadmium plate (on NiCad). The larger the crystals become, the less energy your battery can produce.

The Amp hour (Ah) Rating

I gave the technical definition of an Amp hour above. Now, I’m going to actually explain what that means to you. If you had a 9.6 volt battery rated at 1.3Ah and another 9.6 volt battery rated at 2.6Ah, the 2.6Ah could power the same tool doing the same job two times as long. The best metaphor for the Ah rating is the gas tank on a car. Depending on how you drive a car, if you maintain it and the engine that is in it, your mileage will vary widely, but you’ll always go farther if you have a bigger gas tank if all the other factors are the same.

A Great Resource to Learn About Batteries

I stumbled across a site a couple weeks ago, and using my existing knowledge and some information I picked up there, I wrote this little primer. However, I recommend everyone should go to Battery University to learn from the real experts. Their information is not specific to power tool batteries, but much of the material applies equally to all types of batteries.

Any Questions?

If anyone out there has any questions, I’ll do what I can to answer them, or in other words, yes I take requests.

Matt Griffith

20 Responses to Cordless Tool Batteries – A Primer

  1. Mike in Ojai CA

    Matt, Thanks for the very informative blog about power tool batteries. I’m trying to decide on a new drill, but torn between the one with NiMH and NiCAD batteries. I’ll be keeping it for many years, using mostly around the house, but sometimes for projects needing good endurance. Which type is most likely to give the best long-term performance? Also, is it wise to intentionally drain the battery for storage, then charge it when I need it?
    Thanks ! Mike

  2. Matt Griffith

    Mike,

    I’ll start with the easier question:

    Also, is it wise to intentionally drain the battery for storage, then charge it when I need it?

    According to any of the manufacturers I’ve spoken to about this, you want to store batteries, regardless of the chemical make-up in a fully charged state. All batteries lose charge as they sit in storage. If it gets to a zero charge, the battery could reverse its positive and negative poles (the technical term I have heard for this is “Sympathetic Charge,” basically if there is a cell with more charge next to the cell that is at a zero charge the zero charged cell will align its poles so like charges are next to each other). That is one of many ways a battery can develop a bad cell. You’ll also want to pull out a stored battery every three to six months and throw it on the charger. Storing batteries on bare concrete or metal tends to leech the charge out of them more quickly (probably related to the cooler temperature).

    On the recommendation of a battery technology, there are a number of factors to consider. From what you mentioned you’ll be doing, I’d give a slight nudge towards NiCad mostly due to your questions about storage and concerns about lifetime of the battery. That being said, I think either NiCad or NiMH would work for you quite well, as long as you store it in an area that doesn’t get too scorching hot or freezing cold, and top off the battery every few months.

    Otherwise, the main concern in picking out a good drill to have around the house is the overall quality of the tool. Chances are if the manufacturer cares enough to put on a high-quality chuck and extensively test their ergonomic design, they are less likely to skimp on the batteries.

  3. Brian Mark

    Mike,

    One of the owners of ToolBarn (he’s on the computer side, not the tools side) changed from DeWALT to Makita a while back. He had similar needs to yours in that he doesn’t use a drill often, but he wanted something that was ready when he was and he was certain he wanted cordless.

    His experience was that the DeWALT batteries (Ni-Cad) were always discharged when he went to use his drill. Since changing to Makita (Ni-MH), he hasn’t had that issue.

    I’ve also personally owned the Makita Nickel Metal tools and haven’t had any times where I’ve gone to use a tool and the battery is dead. Even with 4 batteries that I rotate, I have yet to have a dead battery when I go to use one.

    As Matt stated, storage conditions are the biggest issue with discharge. While the garage makes sense for storing tools to most people, that’s a terrible place to keep a battery.

    Supposedly (I’ve not tried storing them yet) the Li-Ion tools have an even lower rate of discharge, so the manufacturers are recommending them for people who aren’t using their tools every day. With some of the rebates right now, you may want to peek at those as well. There are some deals to be had if you don’t mind parting with the money up front.

  4. Mike in Ojai CA

    Matt, Mark,

    Many thanks for the enlightening wisdom about battery choices ! I’m about to replace my old (1992?) DeWalt 9.6V drill. When it was new, I was amazed at the staying power it had. But now the original NiCAD batteries will barely last through driving a half-dozen screws. I always did keep the batteries and charger in the house, and I always just kept one in the charger. Was that a bad idea? It sounds like the NiMH types can have more stamina, than conventional NiCAD. What about the new DeWalt “XRP” NiCADs, and the “BlueCore” by Bosch? Are these too new to know much about?

    Thanks again !

    Mike in Ojai CA

  5. Matt Griffith

    The BlueCore and the XRP are batteries that have a higher Amp Hour rating than the original NiCad batteries that came out. I believe the new XRP’s are 2.6Ah and the BlueCore is 2.4Ah. Basically, the same NiCad technology with a “bigger gas tank.” The NiMH batteries should run longer on each charge, than even these newer batteries.

    I own a two year old Dewalt 18v drill and circular saw. They have worked really well for me. Brian has the 18v Makita and he loves them. If I was in the market for new tools today, I think I’d be looking at Makita (either MXT or LXT series), or perhaps if I had a little time to wait, I might be thinking about Milwaukee’s V18 Lithium Ion tools this summer, depending on how the prices are.

  6. Anonymous

    Matt- dude you rock
    I want to power my 18 volt Dewalt battery tools with a transformer. Can I use a power supply? You are the battery MAN. I want to plug my 18 volt tools into the wall. Transformer and jumper clips or forget about it?

    Thanks- Russell
    (Hvac contactor so. cal.)

  7. Anonymous

    A couple of corrections re: the following quotes “From the early reports we are hearing on the Makita and Milwaukee units, lithium ion seem at least as temperature sensitive as NiMH” Lithium ion performs very well down to -20′C this far exceeds NiMH. You can also charge Lithium ion at higher temperatures.

    “The charging process is much more complicated from a technology standpoint, meaning more expensive chargers or batteries (depending on the manufacturing choices)” Lithium ion charging is easier than NiCad and NiMH. It’s CC/CV with no issues like dT/dt or dV/dt. Just set the voltage and limit the current. You can charge a lithium ion cell with a power supply and a resistor. (do not try this at home!)

  8. Matt Griffith

    For the last two comments –

    Russell,

    I’m sure it is possible to do so, but I certainly would not recommend anyone do so, especially when electric tools are so much less expensive and usually provide more power. Skil actually came out with a cordless tool that had a battery shaped cord set-up (as did DeWalt with their 24 volt line, if you can find it, it is the DW0247), so it obviously can be done… but should it?

    This is a posting about power tool batteries, primarily. Power tools are a high draw and often highly variable power usage application, and this is quite different than the traditional uses of lithium ion.

    There are extra requirements when charging Li-ion in this application that are not necessary for charging NiCad. These include temperature monitoring, even dispersal of charge amongst the cells, etc. Again, for those of you who do not know, early prototypes of high drain lithium ion batteries were highly prone to explosion during charge cycles. This is the primary reason there are diagnostic chips in the tool chargers and/or batteries for lithium ion. There were real and serious safety issues involved in the design of these tool battery technologies. This comes from several manufacturers of the tools that run these batteries, and from at least one of the largest battery companies in the world (who also manufactures tools).

    The temperature sensitivity I mentioned are reports our customers have had in the field, as I stated. Specification, performance and user feedback are difficult to correlate sometimes, and my goal was to pass on the information I had heard.

    Thank you for your input on this. I am not a engineer of any type, nor do I purport to know everything. The goal here is pass on information on battery technology, as it applies to power tools. This is an area that the tool companies have done a poor job on educating the end user, and hopefully, even with some over simplification here and there, this will help the generic builder and homeowner.

  9. Dick H

    Matt,
    I just got two inexpensive 18v, 1.3ah batteries for my portable power drill/drivers. Everything is from Harbor Freight, made in China.The new batteries have only 2 contacts and the old batteries have3. The 3 contact chargers won’t charge the 2 contact batteries. What can I do to alter the chargers (Or batteries) to make them compatible?

  10. Eric

    Matt,
    I heard that all high-volatge Li-ion power tools are not selling well such as Milwaukee 28v, Dewalt 36v and Bosch 36v.
    What I heard is true?
    If it is true, what are the major reasons?
    Eric

  11. Matt Griffith

    Eric,

    We are seeing all the lithium ion cordless tools sell very well. This strong demand applies to the lower voltage and higher voltage battery lines. We are lucky to have well-educated customers and customers who take the time to see what makes the tools different.

    In store settings where consumers have little guidance, such as your average big box store, I could definitely see them not doing as well. Education is an important factor in being willing to spend the big monetary differences between the li-ion tools and their ni-cad / ni-mh predecessors.

    In addition to the cost difference, there are people who feel like they have been burned before when it comes to higher voltage tools. Most of the lines of 24 volt tools that pre-date li-ion were overly heavy, overly expensive and under supported by the tool makers. Early adopters of those tools, I am sure, are less quick to step forward again.

    As more people buy the lithium ion tools, the prices will come down. In a couple of years I expect there will be little difference in price between lithium ion and ni-cad tools of the same voltage. When that happens, it’ll be a no-brainer for people to spend the extra $20 on a tool kit. Until then people will still be wondering if they are better off buying an extra battery for the 18 volt ni-cad / nimh tool.

    Hope that helps.

  12. Anonymous

    Have you heard of repairing or resurrecting old Ni-MH and Ni-CA batteries? Is this for real? or just a pipe dream? They say it will hold a charge again after it was dead.

  13. Anonymous

    Very informative, but I still have some battery issues. I use these tools for a living, and they take alot of abuse. I have a 2 year old Bosch 18v kit that the batteries are dying on; ie: not taking a full charge, short run times. At $90 each, it’s actually cheaper to just buy a new drill, thereby getting 2 new batteries,charger, etc. Seems like a waste. Also, it seems like there are alot of conflicting stories about temperature. I actually read somewhere recently that putting older batteries in the freezer for 48 hrs would “re-charge” them. Then I read another article that said they should be protected from cold temperatures. Finally, why isn’t someone out there re-cycling these?

  14. Anonymous

    Soon after the Korean war was over the US Navy put nuclear weapons on some of their carriers. At that time most of the documents and bomb instrucions were secret. At that time one of the only top secrets was that we used nicad batteries in the nose cone radars of the bombs. At that time the Russians could not figure out how we could equip these bombs with the conventional lead acid batteies.

  15. Anonymous

    Why are two replacement batteries the same price as a new corldless tool WITH two batteries?

  16. Matt Griffith

    Anonymous, you might want to look at this new entry which address your questions The Tool Industry’s Dirty Little Secrets: Replacement Batteries

    Matt

  17. Martina

    Thanks for the very informative blog about power tool batteries.

  18. Andy B

    I bought a Porter Cable 18V NiCad combo and one Lithium Ion Battery, because on the tools they are interchangable. I figured I would have 2 NiCd batteries for the circular saw and sawzall, then I would use the Lithium battery on the drill, to make it lighter and last longer.

    My concern now is charging the Lithium battery. Porter Cable says the batteries are interchangable, but the label on the front of my charger says NiCad.

    Has anyone tried charging Porter Cables Lithium Ion batteries on a NiCad charger. My Lithium battery is still in the package, so I can take it back and exchange it for 2 NiCad batteries.

  19. Matt Griffith

    Andy B,

    You definitely do not want to charge a Li-Ion battery on a charger that is designed for NiMH and/or NiCad only. Most of these batteries should be designed to prevent them from fitting on the older chargers.

    Again, this is a safety risk, so please do not do it.

  20. Scott S.

    I have NiCD 18V Porter Cable batties. Can they be stored on my wooden work bench in my garage where is gets well below freezing in the winter?