4 Common Milwaukee M18 Battery Problems

Battery problems suck, because they stop you from using your tools, even though the tool itself is perfectly fine. Unfortunately, they’re super common too.

Today, I want to talk about some common problems with the Milwaukee M18 battery specifically. If you’ve got one of these and it’s giving you a tough time, one of the tips in the list below will help.

Common Milwaukee M18 Battery Problems

1. Flashing Red and Green

The indicators on a Milwaukee M18 charger flash in a few different ways. While they can only flash red or green, these two colors will shine in different patterns to signal different things.

Out of these patterns, there’s an interesting one that alternates between shining both green AND red. While the Christmas themed lights may look pretty, they’re not a good sign.

This pattern is the rarest out of them all, and the worst one too. It’s to let users know that the charger can’t supply power to the battery it’s attached to.

In other words, there’s something wrong with the battery and it’s not charging. Ideally, the light should just be solid red when charging is going well.

Something being wrong with the battery is a vague thing, though. If you’re lucky, this may just mean that the battery isn’t properly sitting on the charger.

Take it out and push it back in harder, until you feel it click into place. That’s when you know it’s sitting perfectly fine. Do the red and green light still show up after that?

Then that means there is a problem with the battery after all. It’s defective now and not taking in charge. For the sake of both the battery and the charger, you should remove it ASAP.

These lights sometimes show up wrong, and trying to charge your battery at a later time gets it to work. Unfortunately though, it’s likely you’ll need a replacement unless you’re lucky.

But before you buy a replacement, you may like to watch first the short video I made about how you can fix this problem. You can watch it down below.

You will need another good Milwaukee M18 battery. Using a wire, connect the positive and negative terminals of the two batteries.

Let the two batteries stay connected for around 15 seconds. Then, remove the wire and put the battery again on the charger.

Related: Reset Milwaukee M18 Battery Without Charger: Ways I Recommend

You could also encounter a situation in which your Milwaukee M18 battery will blink red when you put it on the M18 charger. I also have a short video about this and you can watch it below.

If it’s a fast blinking red light, it means the hot/cold delay is triggered. This means the battery is either too hot or too cold and you just need to wait for the battery to go back to its normal temperature and try to charge it again.

If you see a slow blinking red light, this means battery charging is pending. The Milwaukee M18 battery charger would only start charging when the first pack of the battery is fully charged.

In this case, you just wait the for Milwaukee M18 charger to charge your battery.

2. Charger Shows Full Power, But No Charging

There’s an odd issue with some Milwaukee M18 batteries. When you put them on the charger, the light turns solid green, which indicates a full battery.

When you check the battery itself though, it’s clear that it has no power in it. It doesn’t power any tools either, obviously. This specific problem is because of the cells.

Milwaukee batteries have a pack of cells inside them, which you can see in the picture below. These should all be at a uniform voltage to work together and hold charge for the battery to power tools.

Due to the heat generated by constant charging and discharging, some cells get hot and self-discharge too much compared to the others in the pack. This is because of rapid charging.

Constantly charging the battery and draining it isn’t healthy for the battery. Not giving it any rest will cause temperatures to rise and lead to the cells becoming unbalanced.

The only real way to confirm this is through a multimeter, and testing each individual cell inside the battery. For a Milwaukee M18, the cells should all ready 4.2 volts if they’re at ideal health.

Individually charge them up until they get to 4.2v if they aren’t already. Place them back into the pack afterward.

Now charge the whole battery to see if it shows the right lights. In case it doesn’t, you’ll know the cells are too damaged and you need a new battery.

3. Fully Charged But Not Working

Is the charger telling the truth and your battery truly is fully charged, but it still doesn’t work with any of your tools? Well, this isn’t as big of a problem as the last one, so don’t worry.

Still, it does need a solution, and I have that for you! All you need, most of the time, is simply to clean the battery up real good. It’s not working because the contact points are filthy.

Dirty prongs stop the battery from working with tools. The prongs on the tool itself can be dirty too. In fact, those are the ones likelier to be dirty if the battery is working fine with the charger.

Simply wiping them off with a cloth or some cleaning spray will help keep them suitable for use with the charger. You can see the prongs on the Milwaukee M18 battery in this picture.

Cleaning should be enough to help with this. Some users might still have trouble, though. If cleaning didn’t help you and you’re one of those users, there’s one other thing to try.

Do you have any spare Milwaukee tools other than the one you’re currently trying? If so, test out if the battery works on that spare tool. Your main tool itself may be problematic

The problem isn’t with the battery but the tool you’re using it on. That’s the only way to explain why the battery isn’t working if it really is fully charged and has clean contacts.

4. Not Holding Charge

A battery that holds no charge no matter how long you leave it on the charger is likely dead. The cells inside no longer have enough capacity to hold more power in them.

This is a common issue, and also an inevitable one. All Milwaukee batteries die out eventually, since they run on lithium-ion cells. That doesn’t happen quickly, though.

It takes years for these things to go bad and start losing their capacity. If it’s been a long while and your battery is past the warranty date, it’s probably too weak and old to power things anymore.

Does the charger show any lights at all when you put the faulty battery on it? Ideally, it should show solid green or red lights like my charger is doing, as the solid lights are good news.

I’ll get to the point, already. Entirely dead batteries can’t be revived like the ones I talked about in one of the previous solutions. There’s no safe and reliable way to get them working again.

Buying a new one is my suggestion. The current one doesn’t hold a charge and isn’t good for anything, so investing in a new one that’ll last you years is the obvious choice.