Does a low battery effect power on cordless tools?

[Sugarfryz]

For example let’s say the battery on my m18 impact is at 50%, will it have less torque than if it was at 100%? I’m only asking because I’m not sure if I’ve ever really noticed a difference on a full, vs depleted battery. Seems to work the same until it dies for me.

I guess just in case, the battery’s are lithium ion and the tool is brushless, if that makes a difference.

 

[The Cobbler]

li-on batteries are less noticeable than ni cd as they discharge
li on has less warning on "dead"

 

[anndel]

Li-ion would just stop when dead but there is a subtle difference in sound/power when the battery is near dead.

 

[James-W]

Li-ion would just stop when dead but there is a subtle difference in sound/power when the battery is near dead.

I agree, but unless you are doing something that requires close to the full power of the tool it isn't really noticeable. At least that has been my experience. I have a Ridgid cordless drill drill with a Lithium-Ion battery. I can be drilling a hole when the battery is almost dead and I will be drilling along normally, then all of a sudden the drill stops dead. I don't notice that the drill isn't as powerful as when it is fully charged because it seems to be the same power level right up until it dies.

 

[Mikeske]

My Makita drill and screw gun it is a barely perceptible loss of power. I can always feel it when they are getting from a full charge to getting close to running out battery power. I am not able to tell with the other brands as I do not own other brands.

 

[shawndp]

On the 1/2 Dewalt 899s at work I can tell the difference in noise when they are coming close to the end of charge - they hit differently. This is more obvious when pulling lug nuts off, but I can hear it going in too. The M18 impact is more subtle and I will usually do a battery gauge check before doing wheels.

 

[DFB]

I've used a non contact tachometer to read rpm speed off of on a few different cordless tools mostly Milwaukee's impacts wrenches and drill drivers and there will be a speed drop up to a few 100 rpm as the battery charge goes down. Overall its really not that noticeable to the eye or the ear or even for performance for most part, but obviously the tool is isn't really at its maximum potential at that point.

The higher the AH the longer run time before drops too

 

[byoungblood]

On my M18 tools, there is a drop in power shortly before the tool stops completely. Usually once it noticeably slows, you may get one or two more pulls on the trigger before it stops completely.

Li-ion batteries don't tolerate being over-discharged, so the tool monitors the battery voltage and shuts off when it gets too low.

 

[6PTsocket]

For example let’s say the battery on my m18 impact is at 50%, will it have less torque than if it was at 100%? I’m only asking because I’m not sure if I’ve ever really noticed a difference on a full, vs depleted battery. Seems to work the same until it dies for me.

I guess just in case, the battery’s are lithium ion and the tool is brushless, if that makes a difference.

There is a thing called a discharge curve. Lithium batteries are pretty flat. Right off the charger they are a little higher than the average voltage, that they quickly drop to. They stay there with very little drop until they are almost discharged and then drop sharply. A half discharge battery should provide full performance. It is that very brief peak value, off the charger that some companies deceptively use to rate their batteries. 12 volt lithiums are 10.8 and 20 volt lithiums are really 18 volts. If it is rated 18, it really is 18.

Sent from my SM-G900V using Tapatalk

 

[PhysicsDude]

As everyone else has stated, there is an effect but with Li-Ion batteries its pretty small. Most "18V" batteries are ~20.x volts at full charge and somewhere around 17 volts when at ~1/4 charge.

So there's a 10%-20% difference in power from full charge to 1/4 charge. I can definitely notice it, but its pretty minor.

 

[American Locomotive]

Here's a typical lithium-ion battery discharge curve:

As you can see, the battery voltage basically remains completely flat for roughly ~70% of the battery's capacity. The voltage is marginally higher for the first 10-20% of the capacity, where it rapidly settles down and stabilizes until end of charge, where the voltage drops off a cliff.

This is why your lithium tools might feel slightly more powerful with a battery fresh off the charger. It's also why lithium tools tend to die suddenly without much warning.

 

[ptgarcia]

In reality, the electronics of the battery/tool should cut off juice before that steep drop off, or at least around it's crest. If not, one risks discharging the battery too far and damaging it permanently. Lithium-based batteries do not like to be over-discharged.

 

[Sugarfryz]

Thank you guys. I was sure I wasn’t crazy when I thought of this. I was told with no-cad it was noticeable though.

 

[topp64]

I think it depends on the tool and what its being used for. I can only speak of my experience with the tools I own. Everything I own is Milwaukee M18 Fuel and the batteries range from high demand 9.0Ah to XC 4.0Ah. I don't think the batteries have any effect on the tools performance, just run-time.

The tool that is used non stop most days on the job is the 7-1/4" circular saw. I do notice a slight difference when the battery is low, but not enough to change out batteries before a total discharge. It's hard to say for sure because I think the sharpness of the blade has a lot to do with it.

My 1/2" hammer drill gets used on the job most days, mainly for drilling 3/16" into concrete. I don't notice any change from low batteries with 3/16 bit. Now and then I'll drill a few 1/2" in concrete and there is a huge power loss when batteries are low. I change batteries when 1 or 2 bars show on battery.

My right angle grinder sees quite a bit of use. Used some on the job with a diamond wheel to grind concrete, used more at home for cutting or grinding steel. There is somewhat of a loss of power and a change in sound when the batteries get low. I usually change batteries with 1 bar showing.

Impact driver I use mainly at home, sometimes at work, never noticed any difference with low batteries.

I only had a couple of months last year with my string trimmer at home, so not many chances to go from full charge to totally discharged batteries. Only time I did battery change was when I started with 3 bars showing, but I did notice a power loss and changed out batteries with 1 bar showing.

 

[kctyphoon]

Short answer - yes, but not a HUGE difference like nicad. and higher amp hr batteries will also result in a more powerful tool.

 

[RoyArms]

Thank you guys. I was sure I wasn’t crazy when I thought of this. I was told with no-cad it was noticeable though.

I find it makes a big difference on the big impacts, 3/4 drive brushless milwaukee. When i am taking big stuff apart and it won't take the bolts loose after a couple seconds of hammering away. Swap batteries and it comes off without any delay, when the battery reads less than full it won't touch them. I've only run into a couple bolts a fresh battery wouldn't take off, took a 6ft cheater pipe on a breaker bar to crack them loose.

 

[6PTsocket]

I find it makes a big difference on the big impacts, 3/4 drive brushless milwaukee. When i am taking big stuff apart and it won't take the bolts loose after a couple seconds of hammering away. Swap batteries and it comes off without any delay, when the battery reads less than full it won't touch them. I've only run into a couple bolts a fresh battery wouldn't take off, took a 6ft cheater pipe on a breaker bar to crack them loose.

That is because, fresh off the charger the battery voltage is briefly higher than the average for the vast bulk of the discharge. The 18 and 20 volt lithiums are the same battery. 2O volts is powering that high powered kick you are seeing but it quickly drops to 18. What they call it depends on the company. If the off peak voltage is not enough to do the job, the tool is underpowered for your purposes. Nobody wants to depend on the first few seconds of run time and it is not realistic to size a tool to a job that it can only do for a few seconds. After the voltage quickly drops to average (18), it stays there until it is almost fully discharged. That is the only realistic way to evaluate the power of the tool.

Sent from my SM-G900V using Tapatalk