Perhaps you should gently take the circuit board and battery pack out of the case to check the voltage for each 18650 cell. It is a snug fit, but they do come out.
Ezio, i think your voltmeter is either wonky or you are not taking the correct measurements. You need to measure the voltage croess indiviual cells which should be around 3.1 to 4.2 volts.
I have been watching the feedback roll in over the last few years and am pleased that Ed’s procedure has helped so many people. The batteries that I have rebalanced years ago are still working. Good job Ed!! Thanks
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.
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.
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?
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!
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?