Let’s try to get some real information about maximizing battery lifetimes and preventing failure. It’s an extremely complicated subject so I’ll try to boil it down. First, some general rules that apply to all common lithium battery chemistries, and then I’ll talk specifically about Makita 18V batteries.
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The most important thing to remember about any lithium battery is to never store it in a discharged state. Recharge it as soon as it’s “dead” and you will avoid many problems.
There is one new feature on the Makita DC18RD dual-port charger. When the battery reaches 80% full, both lights stay on. A lithium battery does not need to be fully charged every time. In fact, you will get more cycles if you do not fully charge it. The battery is happiest when it’s between 20 and 80% full. When the battery is less than 80% it can take more charge voltage input, so thats what the charger does, gives it more. As the battery becomes 80% full, the charger switches to a lower voltage, meaning half of the charge time is the last 20% of power. To maximize battery lifetime you should pull it off the charger before it’s completely charged. This new Makita charger has a both-lights-on indication for when the battery has reached 80% full, when you see both lights steady on, pull it off the charger. This is an important new feature of this charger, if you use it you will extend the useful lifetime of your battery packs.
Putting a lithium battery on a charger while it’s at any random charge level will not harm it. The battery can stay in the charger long-term without harm, but this is a fire risk. Remove it from the charger and unplug it. In 2008 there were a lot of fires and lawsuits, and manufacturers have improved lithium battery safety since then, but there is no type of battery that is 100% safe to be left unattended on a charger. The failure is called VWF – Vent With Flame.
Cold temperatures will not harm a lithium battery. It won’t run your gadgets for as long while cold, but there will be no permanent damage. Still, it’s not a bad idea to bring your batteries inside when the temperature approaches zero F. Lithium batteries can be stored in a refrigerator because the cold will lower the self-discharge rate, but this should be used only for long-term (over six month) storage. Put them fully charged inside a ziplock bag or other airtight container. Never put them in a freezer.
Extreme heat will definitely shorten a lithium battery’s lifetime. Temperatures above 140F° or 60C° should be avoided at all costs.
There are several ways to kill a lithium battery:
- Charge it too fast, at too high a voltage. This should never happen with this charger.
- Overcharge it. Again, this should never happen with this charger.
- OVER DISCHARGE is usually how you kill a battery. More on this soon.
Some further reading:
http://batteryuniversity.com/learn/article/do_and_dont_battery_table#at_pco=smlwn-1.0&at_si=546227c9c0cf4ada&at_ab=per-2&at_pos=0&at_tot=1
Now, specifically about Makita batteries — I’m pretty sure Makita was the first to introduce batteries in an all-lithium format for power tools. So they should get congratulations for that. But now, to retain backwards-compatability we must deal with an out of date cell-balancing scheme.
Inside each 3.0 aH (Amp/Hour) 18V Makita battery case are ten smaller cells utilizing Lithium-Manganese chemistry. The cells are 18mm wide and 65mm long, commonly known as 18650-sized batteries. These are a lot more common than you might think, chances are that your laptop has the same 18650’s inside. They are becoming more common every day in consumer devices & high-end flashlights. Tesla is putting them in those fancy auto-mobiles that drive stock prices to himalayan heights, and Tesla’s “giga-factory” being built in Texas will produce 18650’s. The cells in Makita batteries were made by Sanyo until Panasonic bought Sanyo. Now Makita uses Panasonic, and Sony [Konion] batteries inside some older Makita batteries. Japanese batteries are (in this author’s opinion) consistently the best batteries on the market.
Let’s get back to the problem of OVER-DISCHARGE. Inside the Makita battery there are ten 18650’s, and a small circuit board, called a PCB (Protection Circuit Board). Now I have a long quote from a guy who goes by the handle ToolMon.
“Lithium batteries can burn or explode if abused. They need monitoring, for safety reasons. So Makita put in a smart control board in the battery pack. The control board monitors charging voltage, current, battery temperature, number of charges, and remembers all that. Good idea, right? But… There’s a design bug. The battery control board draws power only from the first cell of the 10 cells in the battery. If you leave it sitting for a while, the control board will deep discharge that first cell to zero, while the others remain charged. To the control board or possibly the charger, that looks like a shorted cell, which could overheat, and the control board remembers it. If you then try to charge the same battery more than 3 times with an apparently deep discharged cell, the conservative software in the control board locks the battery permanently! The control board tells the Makita charger that the battery is unsafe to charge, and prevents charging in the Makita charger. Once “bricked”, the battery cannot be reset.”
Did you get that? The control board consumes a small amount of power, all the time, from only the first cell out of ten. If that first battery voltage drops below 2.5V, the charger reads that as a shorted cell, and will not charge the battery. If you then attempt to charge it a total of three times the control board bricks the battery forever, even though only one cell out of ten is depleted.
Fortunately, there are ways to overcome the bricked battery. You can get an off brand charger that does not read the control board, which can lead to other problems… or use a dangerous way that I won’t discuss here. But the real solution is DON’T LET THE BATTERY OVER-DISCHARGE IN THE FIRST PLACE. Put it on the charger immediately after it’s been used and you’ll never have a chance to brick a battery. Also, charge it if it’s been sitting for a few months, don’t let it sit forever.
Seeing STARS
Another problem with older Makita lithium batteries is the lack of cell balancing. Some cells in the pack could be fully charged while others are not. I don’t have a date for when Makita introduced the “STAR LOGO”, I have tools with the star that predate by a year anything I saw in Makita literature mentioning the star. If your battery and/or tool has either a star or this little yellow tab seen on this battery/charger, that means your pack is cell-balanced. This is a good thing!
See the molded star in the lower-right corner? That, my friends is…
Some tool/battery combinations with and without the star are not possible. I have found that the yellow tab is a better indicator of tool/battery compatibility than the star. If they both have the tab, you’re good.
Another Way to Brick a Battery
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Almost all Makita tools communicate with the battery’s PCB, but some do not. I have around 20 tools, and most of them, when the battery wears down, they keep full power until they suddenly stop. But my little blower is not like this, the motor speed will get slower and slower until I release the trigger. I haven’t tried it but I bet the vaccuum is the same way. I know someone with an early radio, and his will keep playing until the sound is really fuzzy and low volume, but my newer radio will get a little fuzzy for 10 minutes, then suddenly shut off. He says he bricked a battery in his radio when he left it on overnight, mine won’t do that.
DON’T OVER-DISCHARGE YOUR BATTERY!
For safety, Makita leaves some power leftover. The cells could easily be charged to 4.5 volts, but the charger stops at 4.2v… (at least with the older (green) chargers.) This will not only be much safer, it should prolong the life of the battery. I don’t know if this newer black charger stops at 4.2v, or the 80% charge indicator (both lights solid on) means it just hit 4.2v and it is continuing to 4.5v.
Read here if you want to get in over your head:
http://www.candlepowerforums.com/vb/showthread.php?280754-Makita-18V-LXT-batteries/page
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Barry B
Software development consultant in the .NET, T-SQL, MVC, WebAPI, Azure realm. Background in .NET & SQL. Professional research interests in computational cartography, name and address parsing algorithms. Open-source contributor to vCard.NET, and pdfSharp.
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