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I want to run my 12 volt power tools ( ridgid ) using a 12 volt lead acid battery Answered

I have been doing this for years and I finally found this line of tools that is small and compact and the battery fits in the handle and it has tons of power  the lithium ion 12 v ridgid drill and job max line. I tried to wire up the tools contacts to the small lead acid batteries I normally use and even a full size car battery but it failed to power tool because there is this small contact that the tool is requiring which the lithium battery has but obviously the lead acid does not.  I do this for heavy duty use such as continual sawing and sanding and things like that.  any suggestions I really need to make this work as I run a mobile business.  I am looking for a solution to over riding the need for that extra contact and I am fully aware that I will void the warranty as many of you may be thinking. Please help 


I once new a guy who did something like this (sorry, I can't contact him for details), but he waited until his battery had died, and then hacked it.

He dismantled the battery case and removed the dead cells, then drilled a hole in the bottom of the empty case and ran some wires through it to connect to a different battery. Internally he just copied the wiring set up that existed before he hacked the battery, and ended up with a drill that could use the original battery or his "dummy" set up that could be connected to whatever external battery he wanted to use.

The dummy set up duplicated the fit and specs of the original and worked like a dream. No alterations to the drill.
Have you got an old battery to hack? 

How would i be able to replicate the the mysterious third contact that the drill is requiring? I know nothing about this contact nor would i have a way of figuring out what type info it is relaying from batt to drill.
i too used an old battery and gutted the case and did what you are talking about. Only wishing that I could replicate the third contact's signal.

I only know that my friend removed the cells from his battery and kept whatever internal connections/components intact, and relpaced the dead cells with two wires leading to an external battery. Sorry.

I have tried searching for more information about the internal wiring of what I am guessing is your battery.

Just to make sure we are same page here:  The battery is made by Ridgid(r), model number R86048.  The charger for this battery is R86049. The manuals for these, I found here:


The only pictures I have found of a disassembled one of these batteries are here:
That page has some links to some other pages
of other brands of disassembled battery packs, that also look to be based on three 18650-sized Li-ion cells wired in series.

I have a hypothesis regarding that third terminal on this battery pack. My guess is that there is a thermistor,
 basically a temperature dependent resistor, wired in between the third terminal, and the terminal connected to the negative side of the stack of battery cells.

I should probably attach a diagram of this, and give these terminals names: (B+) for the positive side of the stack of cells. (B-) for the negative side of the stack of cells. The third terminal is named (T), and the thermistor is wired in between (T) and (B-).

Using a multimeter, on its voltage sensing setting, the voltage between (T) and (B-) should be zero.  Do that test first, and if you get zero, then, using the resistance sensing setting,  try to measure the resistance between (T) and (B-).

I have tested a few thermistors I have found on other battery packs, and the resistances I found for these were about 7.5K, 10K, and 20K, at room temperature, for the packs I tested .

By the way, if you can manage to get the battery pack taken apart, then you can actually follow the wires, and confirm that they are attached to something that looks like a thermistor.  Also, if  you hold the thermistor between your fingers it will warm up enough to make its resistance decrease a little bit ,and doing this can serve as a method for confirming that component is a thermistor.

Anyway, if the temperature sensor on your battery pack is indeed a thermistor, wired the way I am guessing it is, then you can just sort of trick your drill into thinking its looking at a thermistor, by placing an ordinary resistor between (T) and (B-) having a value of whatever resistance that thermistor has at room temperature.

There also exists the possibility that third terminal might be something much stranger, like a one-wire serial port, but I am hoping it is just a thermistor.

Why do you want to put led acid batteries on your lithium powered tools? They should offer 1.25 Ah. What are your led acid batteries rated at? If they can't offer 1.25 Ah then your better of with the stock battery.

You won't be able to over ride the contact. You will probably need to open up one of the batteries and see what that contact is tied into and duplicate it. It could tie into a charge circuit in the battery pack or be an additional voltage or ground pin.

If you finally found a line of tools that could do everything you wanted but they required the battery to be changed constantly in continuous duty use wouldnt you choose a more efficient medium. Example:
ridgid 's line called jobmax is a one tool system that has about ten different attachemnts that let one tool do anything. I personally am going to use the sawzall attachemnt and the sanding attachemnt for hours on end continusouly for different jobs. Dont think bringing three chargers around with me and plugging them into mains power and continuously swapping them out from tool to charger is a reasonable thing to do. I do all my work away from mains power and do not wish to run my chargers on an inverter due to sine wave and so forth. Not to mention running these batteries into the groun back and forth like this exposes them to lots of cycles and lots of built up heat. I occasionally use 10 amp hour 12 volt agm batteries in a tool belt with a four foot cord when i am moving around alot. I get these batteries for 24 dollars and they have excellent characteristics.

They're called power tools for a reason, and electrical power is the product of two numbers:  voltage and current.


To make this trick work, you will need a battery capable of supplying several amperes comfortably, for as many minutes, or hours, as you've got the trigger pulled. 

I have actually put an ammeter on some DC powered power tools before, and I posted some pictures of that here:
In those pictures the ammeter is the little analog meter, the the yellow needle. Full scale is 8 amperes.
Just based on those experiments, I am guessing the actual number for the current drawn under load,  be something in the range of 5 to 10A.

The mysterious third wire

I do not know what signal is present on this third wire you mention.  But  if you think it is that signal that is somehow stopping your tool from working, then you should probe that signal, and try to figure out what it is doing, if anything.  

Rumor has it, the third wire is for some kind of temperature sensor. I asked Google(r) about the third wire, and it led me here:
among other places.

Sorry if this does not seem like much to go on.


I was hoping not to have to spend tons of time figuring out a way to trick the tool into thinking that it not only has the stock battery in its slot but that that same battery is at proper temp or is sending the confirmation to go ahead and turn on. Since what iam try to do is extremely similar to what many others have already done only difference is that I am doing it on a tool or line of tools that has the battery protection circuit in the tool rather than the battery as many other lithium tools has. this may be common to the 12 volt lithium ion tools as many of their packs are stripped down and small enough to fit in the handle they leave the protection equipment circuitry up to the tool not the pack. I am looking for either:
1. a person who knows all about this and has already accomplished this desired result
2. a person who knows what types of signals that the tool is receiving from stock battery and has a good idea on a reasonable way to replicate, mimic, or trick the tool that it is receving this signal from another auxilary equivalent sized battery/power source.
a: one suggestion that i heard was to open the tool up and force it not to "care" about that dumb signal by bypassing the circuit that picks up that signal. i DO NOT prefer this route because i have multiple tools that i am powering and do not want them to mistreat the stock batteries when they are in the tool as it was originally designed.
b: another suggestion was to mount a stock battery in temporary parallel with the other lead acid battery then run cables from stock battery and its temp sensor allowing the 12 volt lead acid battery to assure the stock 12 volt lithium ion battery never drains. i do not feel very comfortable with this at all seeing as their nominal voltages might be different and they might start "fighting" with each other depedning on the SOC in one or the other.

I have been looking at ryobis line of lithium tools and makitas both of which do not have a third contact on the tool. I have been powering all of my tools in the past with a 12 and 6 volt small agm lead acid battery that i wore in series on a tool belt forming 18 volts but this was inconvenient to replicate and keep charged. i prefer the simplicity of using a line of tools that deisres 12 volt so i can choose all kinds of convenient ways to power them seeing as almost the entire world uses 12 volts as their standard voltage from cars to scooters to backup UPS to battery chargers to you name it. On top of this i finally found a drill that is the size of a small handgun that weighs under 3 pounds that can drive a four inch wood screw in to wood without pilot hole on speed 2 at 1500 rpms and i have invested about 600 dollars in all of ridgids power tools that use 12 volt lithium ion batteries. All the meanwhile assuming that I would be able to do what I have always done and "pick" my own power course other than "shore power" or "mains power". So I am in kind of a bind here and I need an experts opinion on just this issue not other things liike battery power, weight, voltage...... i already know these things. I actually started the whole thing 5 years ago by powering all of my ryobi 18 volt tools with two 12 volts in series and the power was unbelievable because it produced 24 volts with no voltge drop due to load. This success was short lived because the trigger failed after about 45 minutes of cumulative use. this showed me the weakness was in the trigger or variable speed switch. of course i am fully aware the motor will have failed soon thereafter but thats another story. It was fun while it lasted lol