How to Tell if Your Drill Battery Is Bad

Having battery troubles? Yeah, we hear you. Almost everyday, we receive calls and comments about Makita cordless drill batteries that “won’t hold a charge” any more. Maybe you’ve been in that boat before. To clear up a misconception: a battery isn’t like a water bottle. You can’t use up half now, and then wait and use half later. It’s not a tank of electricity. Also, batteries don’t “leak” power like water can. What we’re dealing with here with a lead acid battery is a plastic box that encases a delicate balance of chemicals which are ready to interact with each other to produce electricity when the load is applied.

If your battery is having trouble producing electricity, chances are, it’s a chemical issue.

Here are some ways to test your battery at home, and determine if it’s bad

1) Inspect the Battery

Sometimes you can tell if your battery is bad by simply taking a good look. There are a few things to inspect:

Broken terminal
Bulge or bump in the case
Crack or rupture of the plastic
Excessive leaking
Discoloration

Broken or loose terminals are dangerous, and can cause a short circuit. If a short did occur, there would be some indication of burning or melting. When a battery short circuits, all of the power is unloaded in an instant. That produces a lot of heat, and sometimes even causes the battery to explode.

If the battery is still intact, but there is a bulge in the case, this is usually a result of being overcharged. Others signs such as physical openings in the case are often caused by mishandling. Cracks, splits, and holes will not cause a battery to stop working, but for safety reasons the battery should be labeled unsafe to use.

With wet-cell (flooded) batteries, water levels have to be maintained. If they are low, usually refilling them with distilled water will help. But if the battery has been dry for a long time, it can cause a problem. When the plates in the cells are exposed to oxygen, it rapidly causes sulfation to build up. Sulfation is the number 1 cause of early battery failure. Plus, charging a dry battery will burn it up. If your battery has plenty of fluid in the cells, but the color is dark, or brownish, this is also an indication of a bad battery. Even if one cell is brown, it is rendered useless and therefore the entire battery is, too. Time to replace your Dewalt power tool battery!

2) Take a Voltage Reading

The voltage of a battery is a good way to determine the state of charge. Here’s a handy table with the breakdown:

State of Charge              Voltage
100%                               12.7 – 13.2

75%                                 12.4
50%                                 12.2
25%                                 12.0
Discharged                    0 – 11.9

If your battery is:

Reading 0 volts, chances are the battery experienced a short circuit
Cannot reach higher than 10.5 volts when being charged, then the battery has a dead cell
Fully charged (according to the battery charger) but the voltage is 12.4 or less, the battery is sulfated

Sulfation is the natural byproduct when the battery discharges. Naturally, re-charging the battery will reverse the sulfation crystals and turn it back into electrolyte, ready to produce power again. But if a battery sat, uncharged, severely discharged, and/or drained for extended periods of time, the sulfation will increase in size and harden onto the plates. This covers the surface area of the plates, removing the chemicals needed to produce power.

Sulfation decreases the potential to reach a full charge, and it self-discharges the battery quicker than normal. Charging a sulfated battery is like trying to wash your hands while wearing gloves. At this point, charging alone will not restore the battery to a healthy condition. The majority of replacement battery purchases occur when the original battery has reached this point.

3) Load Test the Battery

Your local automotive shop is more than able to load test your battery for you. But it’s quite easy to do at home. All you need is a digital voltmeter. For any load test to be accurate, the battery must be fully charged. Let’s use a motorcycle battery for an example:

Remove the seat and expose the battery in your bike so that you have access to the terminals. Do not disconnect the battery because you will attempt to start the bike.
Hold the prongs of you voltmeter to the correct terminals on the battery.
Now push the start button and watch what the voltage drops to. It doesn’t matter if the bike starts or not, what you’re looking for is a voltage reading.

A healthy 12 volt motorcycle battery should maintain a range from 9.5 – 10.5 volts under the load for a good 30 seconds straight. If the battery begins to hold and then steadily drops in voltage, there is a problem. If the voltage instantly drops to 0 volts, that is also a problem. We call this the open cell. On a new battery, this can be a result of manufacturing flaws, but it also may be caused by sulfate crystal buildup.

Under the intense heat of the load, one or more of the weld pieces connecting the cells is coming loose and separating. This will cut the current, and voltage will drop. When the battery cools off, the pieces will touch, barely giving a complete connection. This gives you a false voltage reading. Batteries with open cells may read fully charged in idle, but they fail under a load test every time. Once a battery reaches this point, there is no going back. The best thing to do is recycle the thing.

These 3 steps will help you determine if your battery is truly bad or getting there. Sometimes it’s obvious if there is a failure, but other times it’s not. Flooded batteries make it possible to simply look inside the cells and determine if the Bosch cordless drill battery has a physical defect. But for sealed AGM and Gel batteries, it requires testing. The only tools you really need are a battery charger and a digital voltmeter. If your battery experiences any of the symptoms described in the steps above, then maybe it’s time to replace the battery.

Look no further. We’ve got a wide selection of powersports batteries for your motorcycle, ATV, scooter, jet ski, or snowmobile. But we also carry batteries for lawn mowers, wheelchairs, UPS systems, RVs, and marine applications. Whether you need a starting battery or a deep cycle battery, we have the stuff. And all of our replacement batteries come with warranties to ensure that you won’t have any of these problems with your new battery.

About drillbatterycomau

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