This guide applies to Ryobi One+18V Li-ion Battery (130501002), but should also have more general application. This guide will show you how to disassemble the battery pack and check the cell balance and rebalance the cells if necessary.

The battery should normally measure about 18V across the terminals (21V max). If it reads about 12V, then it is likely the battery protection circuit has activated because of cell imbalance. (Those were my symptoms.)

Cell re-balance could also help if the battery isn't taking a full charge (not showing green on the fuel guage button).

The time estimate for this guide is for disassembly and cell balance measurement. Cell rebalance charge time is extra.

CAUTION: Battery disassembly exposes high current circuits. Be careful!

This battery is of 2P5S configuration (sets of 2 parallel cells, 5 sets in a series string). It uses Sanyo 18650 Li-ion cells.

Image 1/2: Remove the four T15 security screws from the bottom. Image 2/2: Remove the one T10 screw on the top.
  • CAUTION: Battery disassembly exposes high current circuits. Be careful!

  • Remove the four T15 security screws from the bottom.

  • Remove the one T10 screw on the top.

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Image 1/2: Using an insulated instrument, lever the battery terminal assembly down inside the top cover. Image 2/2: CAUTION: use of a metal instrument for the above step risks shorting the battery contacts.
  • Lever the cover clips to remove the top cover. Leaver up so the base pops out.

  • Using an insulated instrument, lever the battery terminal assembly down inside the top cover.

  • CAUTION: use of a metal instrument for the above step risks shorting the battery contacts.

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Image 1/2: The battery catch clips on the sides can be removed if you want. Image 2/2: The battery catch clips on the sides can be removed if you want.
  • Once there is enough gap, reach in and hold the battery terminal assembly, while sliding off the top cover.

  • The battery catch clips on the sides can be removed if you want.

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Image 1/1: Cell 1: TP6 to CL1
  • With a Digital Multimeter (Volt Meter) set to DC Volts, measure the cell balance. The nickle straps are good test points. Note the cell voltages.

  • Cell 1: TP6 to CL1

  • Cell 2: CL1 to CL2

  • Cell 3: CL2 to CL3

  • Cell 4: CL3 to CL4

  • Cell 5: CL4 to CL5 (Battery Pos)

  • The cell voltages should be in the range 3.0V to 4.2V. The cells should all read about the same, say 3.9V. If the cells are more than 0.1V different, then cell imbalance could be a problem for your battery pack.

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Image 1/1: Connect the power supply to the cell to be charged up (rebalanced), positive to positive, negative to negative.  Crocodile clips are useful for this.
  • Use a Benchtop Power supply with adjustable voltage and adjustable current limit. Voltage and current meters are necessary too. Example, the Topward 3000 series. Set the voltage to the higher cell voltage you measured, but no more than 4.2V. Set the current limit to 0.5A.

  • Connect the power supply to the cell to be charged up (rebalanced), positive to positive, negative to negative. Crocodile clips are useful for this.

  • As the cell charges up the voltage will rise and stop at the set voltage, then the current will start to decrease toward zero. When the current drops to near zero the cell is charged.

  • Remove the power supply and repeat the cell voltage measurements.

  • Repeat charging on other cells until all cells are within about 0.1V.

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To reassemble your device, follow these instructions in reverse order from step 3.

28 other people completed this guide.


Member since: 08/23/2011

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Using this guide, I successfully dismantled my 18V Ryobi Li-Ion battery with no problem. THANKS edwardb! In my case, I do have cell voltage imbalance exceeding 0.1V (3.48 to 3.36V). I would like to get your feedback on an alternate STEP 5 since I don't have a variable power supply yet. It seems that we recharging the individual pairs of SANYO cells to the same voltage so that the protection circuit will function properly again and allow the reassembled Ryobi battery to be recharged again using the standard Ryobi chargers. If this is this correct, then there might be 2 other options for reducing the cell imbalance to less than 0.1V as mentioned in STEP 5.

OPTION 1: Carefully deplete the cells having the higher voltage to reduce the voltage imbalance to less than 0.1V, or

OPTION 2: Carefully charge the lower voltage cells using a solar panel that has a power rating of less than 4.2Vx0.5amps =2 watts.

Would either OPTION 1 or 2 work?

Al Manzer - Reply

Hi Al, Glad the guide is useful.

Yes your option 1 or option 2 would both work.

For option 1, use a power resistor with sufficient rating (say 10 ohm, 2W). Careful monitoring would be needed. Be sure to stay above 3.0V.

Option 2 should work fine too, might take a while depending on how many cells you can charge while the sun is out (and giving you good power in the solar panel).

Good luck


edwardb -

Ed, thanks for your quick response. This is how I re-balanced my cells. I charged the 4 lowest voltage cell pairs, one at a time, to the same level as the highest voltage cell (3.48V) using a spare 18V Ryobi battery. I connected one cell tab to one terminal of the spare Ryobi using thin bell wire (it's like speaker wire). The polarity is critical (negative-to-negative, or positive-to-positive). I then attached one end of another bell wire to the other terminal of the spare Ryobi. With the free end, I made frequent intermittent contact with the other cell tab. This means touching the wire to the cell tab long enough to see sparks and repeat the contact every 5-10 seconds, depending on how fast the wire heats up. If the wire is hot, then increase the interval between sparking. During this procedure, it is important to monitor the voltage across the cell. In less than a half hour, all cells were charged. After reassembly, I was able to charge the battery up to about 19.8V, a bit less than usual (20.5V). Amazing!

Al Manzer - Reply

How about another alternative: why not use one of the higher voltage cells to charge one of the lower voltage cells? Put two of the cells together with a resistor or series of resistors in between them.

If my EE skills are in tact, you could put a chain of 470 milliOhm 1/4W resistors in series - one for every .1V difference. As the voltage difference drops, remove a resistor from the chain until there is only 1 resistor between the two cells that differ by .1V.

So for example, if one cell was 4.2 V and another was 3.6 V, put 6 of the resistors in series. When they go to 4.2 and 3.7 remove a resistor, when they go to 4.1 and 3.7 remove a resistor until one is 3.9 and the other is 3.8.

Mouser sells these resistors for less than 20 cents here:

Your thoughts?

Kenton - Reply

Kenton, you need to consider your application from the energy perspective. Cells in a Ryobi battery are normally cycled from 3.5 to 4.1V, resulting in 4.8 Wh output/cell. In your example, the 4.1V cell would lose about 1Wh of energy while discharging to 3.9V, based on what I’ve read on the internet. That energy would be distributed to a) the charging of the weaker cell, b) the heat load of your resistors, and c) the charging inefficiencies. For item a), the weaker cell would need about 2Wh charging from 3.6 to 3.8V. For item b), the resistors would dissipate <0.1Wh in one hour at say 0.3 amps. For item c), I would not be surprised if it takes an extra Wh to charge an cell by 2Wh. At the end of the day, you would likely have 2 depleted cells.

Ed’s original intent was to rebalance the cells without removing them from the Ryobi battery. For your approach, you would need to remove the cells if both the stronger and weaker cells come from the same battery pack. Hope this helps. What do you think Ed?

Al Manzer -

Just wanted to say thank you for this tutorial. I don't have a benchtop power supply, but an old cell-phone charger transformer worked perfectly for me. The one I had was 4.8V, 0.9A and I just cut the end off and wrapped each lead around each probe of my multimeter. The multimeter read 4.8V and then I'd touch the probes to the contacts of the low battery cell and the multimeter would drop down to 2.9V (in my case) and slowly trickle up to 3.48V (which was the same as the other cells). It worked perfectly and I didn't even have to have a fancy power supply. Now I've gotta get back to trimming the yard. Thanks again for the ideas!

Damian - Reply

HobbyKing ECO6 50W 5A Balancer/Charger w/ accessories 18.99$ is super for Li Ion and Pb, LiPo, NiCd, NimH, LiFe


Lets you control current (amps) voltage time of charge and much much more.


I use

Turnigy Accucel-6 50W 6A Balancer/Charger w/ Accessories $22.99

Which is almost identical

With ether you can not go wrong.

Ed Hughes - Reply

Thanks for the writeup, very useful information.

I have a P104 18V battery and opened it to test the cells.

All cells are reasonably close. One is 4.1, one 4.07 and the rest 4.06.

So they appear to be reasonably well balanced but I still have issues.

The battery seems to charge fully and shows full bars on the indicator but the battery will only work for a short time and then start dying under load.

When I try to test the voltage across the outside terminals I only get a quick flash reading then it drops to 0. The reading is variable but usually flashes around 19v. Any ideas on what the issue might be? Bad temp sensor in the pack maybe? Any way to test?

Nite Owl - Reply

Nite owl. Did you ever find a solution to your Ryobi battery problem? I have one doing the same 20 volts for a quick burst then nothing. In a tool this will repeat over and over pull the trigger and it runs for half a second then dies

Scott Reagan -

Well Nice Owl, your circuit board could be faulty. Try charging the battery while it is disassembled. If the voltage is 0 at the terminals and full charge at the connections across the cells then it might be the circuit board. Next, to check the temperature sensor, bypass the temp sensor with a jumper wire to see if the battery starts charging normally. If it does then the sensor is faulty. Hope that helps.

Al Manzer - Reply

So where are Cell 1: TP6 to CL1

Cell 2: CL1 to CL2

Cell 3: CL2 to CL3

Cell 4: CL3 to CL4

Cell 5: CL4 to CL5 (Battery Pos) ?

I'm new to this but I have two dead although new maybe two charges,and one never worked. And how do you charge each cell? I don't have a Benchtop Power supply with adjustable voltage and adjustable current limit.

daddywoofdawg - Reply

WORKED PERFECTLY with cell phone charger THANK YOU ,THANK YOU ,THANK YOU!!!!!!!!

Frank O - Reply

I was also able to rebalance my battery using this guide and a cell phone charger. I do have one P107 (battery with fuel gauge) that is completely gone. I was considering buying a P102 and using the cells in the p107 so I can keep the fuel gauge. The p102 is about half the cost of a new p107. Has anyone done this or think it is possible?

John - Reply

It's very possible, the difference being 102 has 11865 cells and 107 has 21865 cells, so basically what you will have is a 102 with a fuel gauge.

Dmac3009 -

I have a question. I have a p108 that is fully charged each cell at 4.2v and all cells together measure 21v but at the upper terminals i only get 16v. Now obviously its a problem somewhere on the board but does anyone have a clue which component could be reducing the voltage?

john - Reply

Also useful if you leave your battery uncharged for a long period of time, a year or more, the defective light will come on not allowing the battery to charge. If this happens the battery has been totally discharged to the point where the charger can not determine if the battery is inserted. Try putting a 12 volt battery charger to the Positive and negative points on the battery for a minute. It will charge the battery enough so that the charger will recognize the battery is installed. Essentially re-polarizing the battery. Just did it to my father's kit with 2 batteries. My Dad passed away nearly 2 years ago and I was cleaning out his garage and found the 4 piece kit. The Batteries had not been charged in at least 2 year. Deader than a door nail. Re-polarized the 2 batteries and "Walla" they took a charge. The tools are working great.

jerryschutz - Reply

Dude, sweet! I thought I was going to have to throw out a three-year-old battery, but this little tip saved me. Sad that Ryobi didn't implement automatic battery balancing, but hey, you gotta do what you gotta do!

Erik Ness - Reply

My question is how do you open the battery pack that seems to have a security cover over one of the five screws? I have a Ryobi P102 battery pack

Stan - Reply

Hi Edward or anyone else. Both my batteries never charge or go green. Just the red slow pulse when I plug them in charger. If I let them sit in charger for a while they get up to 16.32v. Not much higher and work to turn the drill for 5 sec then it dies. So I tried this guide and measured the volts across all the points specified above but they don't look to be more then .1 v variance.

Tp6-cl1 =3.25

Cl1-cl2= 3.22



Cl4-cl5=fluctuates between 3.29-3.30

Is that still the case or do I have something else going on. Maybe bring them all up to 3.30 and see if that's the issue?

Michael Spivack - Reply

Hi Michael. It seems that you may have 2 issues. There is likely a problem with your charger. I have 4 old (different model) Ryobi chargers and 16 old batteries. I find that not all chargers will charge all my batteries, ie, some batteries will only charge on one or two chargers. I also have some batteries that appear fully charged (green light) and will only work for a few minutes before being depleted (red light), I've set these batteries aside and will swap out the 18650 cells on a cold snowy day next winter when I have more time. Meanwhile, you could try charging all 5 cells individually to about 4.00+/-0.05 V, then reassemble and try your drill. If your drill only works for a few minutes, then the problem lies with the cells and you can try swapping them out with newer cells. If the charged battery works fine, then you probably have a faulty charger. Good luck.

Al Manzer - Reply

This actually works. I also used an old phone charger plugged into a AC wall socket and wrapped the wires around a multimeter test probe to recharge each cell. I charged each cell back above 3.3 volts. The Ryobi charger took it from there. I did alot of research before doing this. The chip board in the battery must not allow the charger to charge "excessively depleted" cells in a pack to protect against fires. I use R/C cars with lithium batteries. Supposedly any voltage drawn below 3 volts per cell damages a lithium cell. Make sure you have the correct polarity when touching the cells or POOF!

Cael Sprute - Reply

Hi, One of my two P104 Ryobi batteries has a malfunction. I took the pack apart and found that the last two cells (Battery Plus edge) had a reading of -0.7Volts. I replace the two cell group with purchased cells and still the battery will not charge. The central terminal (of the battery pack) reads about 8 Volts while the two positive and the + to - tabs also reads about the same 8 volts. The battery plus to battery minus solder taps on the PC board reads about 16 volts. The FET Q8 may be a problem. The approximately 8 volts is present on the Gate pin and the Drain pin. I am in the process of trying to trace the track on the PCB and find out why the anomalies are there, however I am finding it very difficult without a schematic. Do you by any chance can direct me to a site or some one who may have a schematic of Ryobi PCB P/N280079004/280079009.

Chris Mallios-August 12

Christos Mallios - Reply

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