Which Battery Pack Has More Capacity as a Power Bank?

[easysurfer]

This isn't a trick question, but one I'm trying to figure the answer to.

I have a RavPower bank and a Milwaukee drill battery. I also have an adapter which snaps onto the Milwaukee so it can charge USB devices.

My feeling is there'd be more capacity with the Milwaukee than the RavPower, but I'm not sure how to compare by looking at the specs. See photos of specs. (The blurry photo on the Milwaukee shows 18V, 54wh ).

 

[travelover]

Watt hours are the units of comparison.

 

[easysurfer]

Watt hours are the units of comparison.

In other words, the Milwaukee has more capacity because of the higher watt hours?

Seems most power banks tout mAh and don't mention watt hours.

 

[NW-Bound]

In other words, the Milwaukee has more capacity because of the higher watt hours?

Seems most power banks tout mAh and don't mention watt hours.

Yes.


To convert mAh to Wh, first you divide by 1000 to get to Ah.

Then, multiply the Ah with the voltage in Volts. The result is A.V.h or Wh, as amp * volt = watt.

The nominal voltage is usually a multiple of 3.6V, depending on how many cells are wired in series inside the pack.

For LFP cells, it's 3.2V/cell, but I don't think power tools use LFP cells.


PS. In the case of the power pack, it has an internal DC-DC converter which outputs 5V. The 5V is not the native voltage of the internal cell. And then, the output of 1A is the limit of the DC-DC converter, which also has nothing to do with the storage capacity of all the cells.

The RAVPower label says 10,400 mAh, 38.4 Wh. The cell voltage is obviously 3.6V, because 10.4 Ah x 3.6V = 37.4 Wh.

Some makers claim their cell nominal voltage is a tad higher than 3.6V, thus the 38.4 Wh.

 

[travelover]

In other words, the Milwaukee has more capacity because of the higher watt hours?

Seems most power banks tout mAh and don't mention watt hours.

As NW explained, amp hours don't take into account the voltage, so to compare, you need to convert to watt hours for a true comparison.

 

[NW-Bound]

Another thing to note: Cell storage capacity should not be confused with cell power.


There are generally 2 classes of lithium cells: energy cells, or power cells.

The energy cells are generally used in cell phones, laptops, and other electronic devices. They are built to store a lot of energy for a long run time.

Power cells are built for very high discharge rates for use in power tools. In exchange for the high power, their capacity is often only 1/2 to 2/3 that of an energy cell, for the same volume.

The difference is the same as that between a marathon runner and a sprinter.

 

[Out-to-Lunch]

One factor not touched on above is the efficiency of your USB adapter. It is likely to be highly efficient, so that you can blithely compare the Wh of the two storage cells. However, it is possible that you could have purchased a converter that is inefficent in converting 18V down to USB voltages, in which case you need to derate the Wh figure from Milwaukee by the efficiency number of your converter.

 

[easysurfer]

Thanks for the replies.

I ordered a geeky tool to measure USB ports. Tool will show both mAh and Wh .

I have too much time on my hands.

 

[easysurfer]

My USB measuring [-]toy[/-] tool arrived.

Do I need? Definitely not.

But it actually may come in handy to measure if I think a drill battery, for example isn't keeping a charge. Better to measure than go by guessing.

 

[NW-Bound]

Yes, that's a nice one and it will prove useful.

I have a cheap Chinese dongle one, and I don't know how accurate it is, but when it is inserted in line with a USB AC adapter/charger and a device getting charged it can tell me if a current is flowing.

Prior to having it, I was driven mad with bad USB cables that had an intermittent contact. My wife would plug in her notebook or phone, and came back a few hours later and saw that the device did not get charged. The cheap dongle will tell me how much current is flowing, and even if the measurement is off, it is still useful.

 

[easysurfer]

Yes, that's a nice one and it will prove useful.

I have a cheap Chinese dongle one, and I don't know how accurate it is, but when it is inserted in line with a USB AC adapter/charger and a device getting charged it can tell me if a current is flowing.

Prior to having it, I was driven mad with bad USB cables that had an intermittent contact. My wife would plug in her notebook or phone, and came back a few hours later and saw that the device did not get charged. The cheap dongle will tell me how much current is flowing, and even if the measurement is off, it is still useful.

Does your one retain the values when off?

The one I have by Klein is ranked as one of the top ones (Klein makes expensive tools ). But it doesn't automatically retain the values. Which is one of the negatives.

So, say, if a power bank senses a phone is fully charged, the power bank may stop sending energy and as a result the Klein device shuts off.

There is a memory function however, where while in progress, I have press a button and capture the data in memory to retain. (10 memory locations before overwriting). This is a manual process.

At this moment, I'm monitoring a power bank that's charging my phone. The device is handy as I didn't know the USB of that power banks only uses .48A. Now I know .

 

[Time2]

Two things to note, some manufacturers let the sales dept rate their battery.
Batteries degrade with use and/or abuse.

 

[easysurfer]

I've been charging a phone for almost 4 hrs.

From 10% full to now about 40% full.

So far, used about 9 Wh .

 

[NW-Bound]

Does your one retain the values when off?

Yes it does. Not bad for something that costs me a few dollars off AliExpress.

After seeing that it worked, I bought another one just for a 2nd "cable connection verifier".

 

[Jerry1]

Now I want one of these meters but I just don’t think it will be that useful. Interesting and a cool toy but not too useful. I’m inclined to get the cheap one but I love Klein Tools.

 

[easysurfer]

My first try, the battery pack didn't last as long as I thought and went out before I could take a look at the numbers. I do see that as a weakness with the Klein. I do know that the power bank I had plugged in can't charge my phone fully. Only about 1/2.

Of course, I could have determined that too without the meter.

 

[Time2]

For measuring battery capacity, I think you might want a load tester such as this.


https://tinyurl.com/35y2ftde



Or



https://www.amazon.com/150W-Electro...attery+capacity+tester&qid=1658062971&sr=8-11

 

[easysurfer]

Back to the drawing board for me.

Decided to return the Klein and get one of those cheaper ones.

I really liked the Klein except the info not saved at power off is too much a deal breaker for me.

The one that does capture info at power off should arrive on Wednesday .

 

[ERD50]

Back to the drawing board for me.

Decided to return the Klein and get one of those cheaper ones.

I really liked the Klein except the info not saved at power off is too much a deal breaker for me.

The one that does capture info at power off should arrive on Wednesday .

Probably the right move, but in some cases like that, I've set up an old digital camera or phone to take a video. They usually can capture several hours worth.

Not something you want to do routinely, but it's an option.

-ERD50

 

[easysurfer]

Yeah, could record or set up time lapse photography.

But more trouble than worth.

 

[easysurfer]

Bought a different tester, but that was defective.

Maybe should have just quit when behind and kept the Klein (though it didn't do exactly what I wanted).

Or maybe, I really don't need such a gadget after all .

 

[Time2]

Bought a different tester, but that was defective.

Maybe should have just quit when behind and kept the Klein (though it didn't do exactly what I wanted).

Or maybe, I really don't need such a gadget after all .

Here another constant current load tester to try,

https://www.mpja.com/07-21-22.asp?r=291490&s=5

Watch the video and read the reviews.

 

[NW-Bound]

Here another constant current load tester to try,

https://www.mpja.com/07-21-22.asp?r=291490&s=5

Watch the video and read the reviews.

The above does not provide a cumulative Wh measurement.

 

[Time2]

The above does not provide a cumulative Wh measurement.

OK, I have this one, https://www.amazon.com/SKYRC-Balanc...658415419&sprefix=SkyRC+B6+Imax,aps,95&sr=8-3


Although I think the discharge current is a bit limited, but it certainly has all the bells and whistles.

 

[easysurfer]

I've been regrouping.

Bought 3 new USB testers and a dummy load.

Tester #1 - a cheapo (but nice) for about $7. Does not show Wh but retains information.

Tester #2 - Klein that only does USB-A. Suffers same lack of feature as the other Klein in not retaining information when power drained.

Tester #3 - A better than cheapo tester that keeps track of both Wh and mAH.

Tester 1 and 2 have arrived. Tester 3 should arrive on Sunday. The dummy load on tomorrow.

I haven't opened tester #2 as will probably return if Tester #3 works fine. Tester #3 seemed complicated at first. So thought I could get by with #1 and #2. But saw a youtube video on how to use #3 and didn't look so bad, so I bought that also.

When all the dust settles, there actually is some use for this madness. I'm curious to see how good and old drill battery is that I carry in the car for my cordless inflator.