The most common reason a Ryobi 18V battery won’t charge is that one or more of the cells have been discharged too far. This causes the battery to go into what is known as sleep mode.
The charger cannot detect the battery to check its health and won’t risk charging it. You will usually see the charging unit lights flashing red and green in this instance.
The Battery Pack is Out of Balance
Your Ryobi 18V battery pack is made up of many individual cells. If the cells are out of balance and hold different charges, this could cause a problem. There are a few possible causes of a cell failing:
- The cell can no longer hold a charge.
- The cell will not accept a charge.
- Individual cells will charge and discharge at a different rate to other cells. If the difference is large, then one cell will be out of the other cells’ voltage range. This is particularly noticeable in old battery packs.
- Voltage drop under load. Most tools have a built-in low voltage cutoff. If the battery falls below the cutoff level, the device will not work. Out of balance packs may exhibit this issue, preventing the tool from operating.
There are some ways to fix an out-of-balance battery pack, and we discuss them now.
How to Fix: Charge Just One Cell
If your battery pack is still under warranty, don’t try this. Send the pack back for repair or replacement.
To charge a single cell, you must open the battery pack. You can now check each cell voltage, and if required, charge the cell individually with a bench power supply. The aim is to charge all the cells within 0.1V of each other.
Once all the cells are charged, you can reassemble the battery pack and try charging it again.
Click the link for more information about rebalancing a Ryobi 18V battery.
How to Fix: Jump Start from Another 18V Battery
If your battery pack has been over-discharged, the battery’s charging circuit will probably prevent it from charging. To recover the battery, it’s possible to use a healthy 18V battery to “jump-start” the bad one.
The method involves connecting the good battery to the bad battery for a few seconds. This gives the bad battery a temporary charge that will fool the charger into working.
- Remove the battery pack outer casing so you can access the individual batteries.
- Identify the positive and negative terminals on the battery pack.
- If you have a multimeter, measure the voltage at the terminals. It will probably be very low.
- Using a known good battery, connect it to the bad battery. Positive to positive, and negative to negative. Connect directly to the batteries and not through the control circuit board.
- Leave them connected for 20 or 30 seconds.
- If you have a multimeter, check that the bad battery pack’s voltage has now increased substantially.
- Reassemble the battery pack and put it in the charger.
- If the process has worked, the battery should now charge okay.
This how-to jump-start a Ryobi 18V battery video explains the process very well.
Your Battery Is Bad
Your Ryobi 18V battery pack contains several smaller batteries connected in series. If just one is bad, it can make the entire battery pack unuseable. We can check the individual batteries using a multimeter.
Checking the battery is just a few easy steps:
- Charge the battery for at least an hour
- Measure the voltage by connecting a multimeter to the battery terminals.
- The voltage reading should be higher than the battery rating stamped on the side. If it’s below this, the battery needs to be replaced.
Batteries can show a good voltage with no load, but the voltage can fall dramatically as soon as you apply a load. A fully charged battery pack that only powers your tools for a short while may indicate a bad battery.
This great video on how to test and replace batteries in your Ryobi 18V pack is handy.
There are a couple of possibilities here:
#1: Battery pack connector. Where the pack plugs into the charger, the battery contacts may be damaged or bent. These can be carefully bent out a little using pliers to ensure a good connection.
#2: Internally, your battery pack contains several individual batteries, soldered together. There may be a loose connection, or one of the solder connections may have come loose.
#3: Make sure you are pushing the battery firmly into the charging unit. The red charger light will flash continuously if the connection is not good. You should hear a click if the battery is inserted correctly.
The Battery Is Too Hot/ Too Cold
The charger and the battery pack both contain checking circuits that monitor the battery.
If the battery becomes too hot or too cold, charging will be stopped. Temperatures below around 50°F or above 100°F may prevent charging.
Move the battery and charger to a room temperature location. Allow them to acclimatize for a while and try charging the battery again.
A Simple Way to Recover a Non-Charging Battery
One method that seems to prove useful in recovering a battery is “shock” it. This is a simple process and has recovered many batteries without the need to dismantle the battery pack:
- Put the battery into the charger.
- Using the mains connector, quickly plug in and unplug the charger. Try to achieve a speed of two or three times a second. After about 10 or 15 seconds, leave the charger connected. Hopefully, the red charging light is now on.
- If this does not work the first time, try it for a few attempts. If it doesn’t work, then refer to the testing and dismantling options described above.
Tips for Maintaining Ryobi Battery Properly
- Charge your battery where the room temperature is between 50°F and 100°F.
- Store your batteries in a dry area where the temperature is not too hot or too cold.
- Regularly check your batteries. They need to be charged every four to six weeks if you are not using them. This will maintain them in the best condition possible.
- Remove the batteries from the charger after charging. Although the charger may have a cutoff, it could fail and overcharge the battery.
- Batteries get hot during use. It is recommended that you allow them to cool for a short while before charging them.