# Modify old Makita cordless saw to fit new battery



## jgibbs

I have an older cordless Makita circular saw (model: BSS611) I bought with a set of Makita cordless tools. One of my batteries died and I bought a newer 4.0 amp battery (the 5 amp batteries are still quite pricey) and a new charger (model: DC18RC) because Makita says the 4 and 5 amp batteries should not be charged on the old one (model: DC18A). The new battery fits all my old tools except the circular saw, even thought I bought them all as a package. I did the research and I know about the "yellow connector" and/or "star" on the connector plate of the tool which indicates it is compatible with the new battery type. My saw does in fact lack this indicator while the other tools have it. 

There is a small lug on the saw connector plate that prevents the new battery from connecting. I have read some internet posts from individuals that say they ground off the lug and have used the new battery on the old saw. There are some industry website posts, going way back to when Makita first intruduced the 18V 3.0 amp battery, that say the saw was manufactured with the saw to prevent its use with the even older 1.5 amp battery because the saw would overheat the 1.5 amp battery which was intended only for certain lighter duty tools. If this is the ony reason for the lug, then it would seem harmless to remove the lug since the 5 amp battery could easily handle the load. However, newer information from Makita talks about how the "yellow" and "star" marked tools have computer chips which somehow talk to a computer chip in the new batteries to somehow prevent damage to the battery and extend its duty cycle and life.

So, my question: Is there any harm in modifying the saw connector so it accepts the newer 4 and 5 amp batteries? Is the Makita claim about the computer chip preventing damage really true? If so, why does the battery fit my old hammer drill and impact driver? Certainly they don't have the computer chip since they were manufactured long before the 4 amp battery was on the market. Howe much of this is true and how much is manufacturer hype?


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## wptski

If you going to a larger amp battery and as long as your not making a electrical modification to saw, I see no problem. I like and do stuff like this all the time.

They always like you to buy new stuff! I remember years ago on dot matrix printer cartridges drilling a hole to use a different one.


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## Mort

I don't see a problem. Of course, you can't charge a lithium battery on a NiCad charger but the tool doesn't care what kind of battery powers it. 

We have Makita cordless at work and the angle grinder is like that. It's really irritating.


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## jgibbs

Thanks for your answers. What do you think about Makita's line about a computer chip in the newer tools communicating with a chip in the battery to protect the battery. Could the tool damage the battery?


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## woodworkbykirk

the newer batteries deliver more power to the tool.. the older tools have lighter gauge wiring in them which will overheat and catch on fire if you use the newer batteries.. thats why they issued teh public notice about the star on the tools. so that you dont put yourself at risk


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## jgibbs

@woodworkbykirk - Thanks, that makes sense. More amps means if you push the saw hard it could draw more current that it was designed to handle, causing it to overheat. Since the old saw doesn't have the computer chip it can't tell the battery when it is being overdriven. I guess if you altered the saw to take the higher amperage battery you could prevent damage if you were careful to not push the saw. But I'm the kind that pushes my tools to the max. Of course, if I burned out the old saw that'd be a good excuse to tell my wife I need to buy a new one :wink2:.


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## mikegp

I modified a Makita reciprocating saw to fit the newer battery. Been using it for 3.5 years with no issue. Batteries are close to 5 years old now and still work as well. 

Here was my thread asking about it:

http://www.diychatroom.com/f29/modifying-makita-reciprocating-saw-use-diff-battery-bad-idea-137791/


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## jgibbs

@mikegp - Thanks, my initial search didn't find your 2012 post. The big difference from my question is that your saw, that came with a 3.0 amp battery, would not accept the newer *smaller * capacity 1.5 amp battery. I have the sort-of-opposite problem: My saw came with a 3.0 amp battery and it won't accept the newer *larger* capacity 4.0 and 5.0 amp batteries. If I understand correctly, your concern was whether your saw would damage your battery, where mine is whether the battery will cause the saw to damage itself.

However, your thread has some interesting points. Paraphrasing a bit: One reminded me that "amps are amps and volts are volts" i.e. it is the tool, not the battery, that determines how many amps are drawn at any given time. Another post noted that a 3.0 amp rated battery means amp-hours - it is rated to last one hour at 3.0 amp draw, not that it will supply a max of 3.0 amps. Another post noted that, according to Ohms law, the tool will draw whatever amps it requires at any given point. The harder you drive the saw the more current it draws (volts x amps = watts, volts is given so amps increase). The hotter the saw gets the more amps it draws. 

So...from based on my limited experience with electricity from DIY house wiring, following is what I think I've learned from this thread. If there is an electrical engineer out there, I would appreciate if they coul verify whether I know what I'm talking about:

The hazard to the saw presented by modifying it to accept a larger capacity battery is that you can push the saw at high amp draw for longer than it was designed. Thus the tool's smaller gauge wiring can heat to the point beyond the tools ability to dissapate the heat, causing the wiring to burn, damaging the saw and possibly catching fire. Makita claims that their new batteries and tools come with computer chips that monitor the current draw and prevent damage to either the tool or saw. So it seems to me that their claims are not entirely marketing hype.

Thanks all for your contributions.


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## woodworkbykirk

jgibbs said:


> @*woodworkbykirk* - Thanks, that makes sense. More amps means if you push the saw hard it could draw more current that it was designed to handle, causing it to overheat. Since the old saw doesn't have the computer chip it can't tell the battery when it is being overdriven. I guess if you altered the saw to take the higher amperage battery you could prevent damage if you were careful to not push the saw. But I'm the kind that pushes my tools to the max. Of course, if I burned out the old saw that'd be a good excuse to tell my wife I need to buy a new one :wink2:.



youll not only fry the tool youll fry the battery as well since the older tools dont have the chip that will shut the tool down if its overloaded


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## wptski

jgibbs said:


> The hazard to the saw presented by modifying it to accept a larger capacity battery is that you can push the saw at high amp draw for longer than it was designed. Thus the tool's smaller gauge wiring can heat to the point beyond the tools ability to dissapate the heat, causing the wiring to burn, damaging the saw and possibly catching fire. Makita claims that their new batteries and tools come with computer chips that monitor the current draw and prevent damage to either the tool or saw. So it seems to me that their claims are not entirely marketing hype.
> 
> Thanks all for your contributions.


You aren't modifying the motor in the saw but the size of the battery. The motor will only draw so many amps. Increasing battery size is nothing new as it's done all the time. Look at the DeWalt 20V Max batteries, 2Ah, 3Ah, 4Ah and 5Ah. As far as the chip, I'm not sure what it protects. You can put a 650 CCA battery in your car that has a OEM 550 CCA battery. You could also put more than one battery in parallel as that's what tow trucks have and how they can overcome a shorted battery in one's car to get it to start when you can't.

I once ran a DeWalt 14.4V angle drill with 3M Scotchbrite pads non stop other than swapping batteries till I could hardly hold on to it because it was so hot.

Marketing claims? A DeWalt 20V Max is just a 18V read at no load!


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## jgibbs

@wptski - I hear what you're saying. But your analogy to a car (or even to Dewalt tools) may not be complete. For one thing, battery leads to the starter and frame are thick and undoubtedly the starter is de-rated relative to the battery leads just for the purpose you mention. And auto starting systems are designed for brief periods of high amp service. Sometime when your engine won't start, try cranking the starter for several minutes non-stop. I gurantee you the starter will start smoking. Do this often and you'll be buying a new battery. 

There may not be as much margin of error in the tool wiring, particularly the motor windings. I'm not necessarily disagreeing with your conclusion. Maybe you could get away with a 5 amp battery on an old Makita tool, run it hard until the battery dies every time and maybe get years more use from the tool. Or maybe not. It's hard to prove outside of a test lab environment.
And in my opinion, running your tool until it is too hot to hold is probably damaging the tool. Not saying it will immediately fail, but your probably shortening it's life.

This is part of the reason for my post. I wanted to see what other people's experience with electrically over-rating a tool. And I needed to be reminded of how electricity works. I still don't get the computer chip thing.

Judging from the response to my post, opinion seems to be equally divided between "It's not a problem, just Makita marketing hype" and "If you do that you'll fry your saw." So not much learned there. Still waiting to hear from an electrical engineer.


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## wptski

jgibbs said:


> Still waiting to hear from an electrical engineer.


Why wait for an electrical engineer which may never happen in this forum? Go to them here: http://www.eng-tips.com/


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## mgp roofing

My boss ran into this same issue about 6 months ago--new 4.0ah battery would not fit an older Makita metal nibbler that gets used to cut metal roofing sheets. The technician in the shop said to grind off the lug on the battery that stopped it fitting. We did that, and it works fine. That battery is fine with all our other tools too.


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## emcalnan

Electrical Engineer
The 1.5 amp-hour battery uses a single group of five *18650* cells. The five cells are connected in series.
The 3.0 amp-hour battery uses two groups of five *18650* cells. The two groups are connected in parallel.
Because it uses two groups of cells connected in parallel the 3.0 amp-hour battery can deliver more current without overheating.
I agree that the tab was a good idea to prevent the use of the 1.5 Ah battery in tools that use high current - like the circular and reciprocating saws.
It is not clear why Makita prevents the use of the 5 Ah battery on these older tools. The tools won't draw more current from a 5 Ah battery than they would from the smaller capacity batteries.
In any case the aftermarket 5 Ah and 6 Ah batteries I have used do not have the extra high ridge of plastic that prevents inserting the battery in the older tools. I have been using aftermarket 6 Ah batteries with the circular and reciprocating saw - among other things - for years without problems.
All the higher capacity batteries (3Ah or more) have the same construction, two groups of five cells, and thus can deliver the same amount of current. While it is nice to have the extra circuits on the newer tools that can detect overheating and shut the tool down we survived without that for years, at least I did, and never had a tool or battery fail, burst into flames, etc.
The older tools are probably way past their 3 year warrantly so I agree with "mgp roofing" - cut the tab.


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## chandler48

@emcalnan It's a 7 year old thread. Just for information, though, on Makita batteries, they also changed the contact number and location, so short answer is No, they can't be retrofitted.


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## emcalnan

Thanks Chandler48. I purchased two 5.0Ah Makita batteries from Home Depot last weekend (12Nov22). These batteries did not fit in most of my tools - such as the circular and reciprocating saws - so I Googled around and found a few "threads" that covered this topic - such as this one. I don't think anything has changed in seven years. The brand new Makita 5.0Ah battery would not slide into my old tools - so I cut the tab. If the contact number (1, 2, or 3?) changed and the location of the contacts changed these changes did not appear to affect my tools or the fit of the new Makita BL1850B batteries - once the tab was cut off. My good old BL1830s have three contacts in the same position as the brand new BL1850Bs.
As I was researching this topic I ran into some great YouTube videos on the subject of 18V Makita batteries. Seems to be a popular topic even in 2022.


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## raylo32

It is easier to modify the batteries than the tools. Just take a Dremel and grind down the tab on the battery that stops it from inserting. I run the new batteries in several of my older Makita tools, no problems at all.

In the photo below the 4.0 Ah battery on the left has been modified and the 5.0 on the right not.


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