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Old 06-21-2018, 10:01 PM   #1
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Battery question

So this is not necessarily boating related, but I have a question regarding my cordless tool batteries, and I know there are so really knowledgeable folks here. Sooooo....first a picture:
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Old 06-21-2018, 10:05 PM   #2
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and now the question: Both of these 12V batteries are rated as 3.0 Amp hour batteries. Logistically that seems odd due to the difference in size. But here's the part that really confuses me: The smaller batter is rated at 36 watt hours...and the larger battery is rated at 32 watt hours. So my questions are....

If the voltage is the same, and both batteries have the same amp hours...shouldn't they have the same watt hours ?

And all I care about is run time...should I focus on watt hours or amp hours ?


Why doesn't size matter.....the smaller battery has a larger watt hour rating ?


Thanks in advance.
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Old 06-21-2018, 10:15 PM   #3
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and now the question: Both of these 12V batteries are rated as 3.0 Amp hour batteries. Logistically that seems odd due to the difference in size. But here's the part that really confuses me: The smaller batter is rated at 36 watt hours...and the larger battery is rated at 32 watt hours. So my questions are....

If the voltage is the same, and both batteries have the same amp hours...shouldn't they have the same watt hours ?

And all I care about is run time...should I focus on watt hours or amp hours ?


Why doesn't size matter.....the smaller battery has a larger watt hour rating ?


Thanks in advance.
Looking at the shape I am not sure these two are much different. I may be wrong but looks like the batteries are inside the 2 red cylinders. The base black plastic may just be empty. A good way to compare, are both the same weight?

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Old 06-21-2018, 10:16 PM   #4
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If they are 12v and 3.0 Amp hour, then by definition they are 36 watt-hours.
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Old 06-21-2018, 10:20 PM   #5
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the smaller one is 6.7 ounces and the larger one is 14.3 ounces

I would have thought the same thing..same volts, same AmpHours = Same watt hours.

I am about to buy 2 more and am wondering if I am just paying for a psychological factor of bigger size.

If we really wanted to complicate the issue...the larger battery comes in a 4.0 or a 6.0 Amp hour rating...and the smaller one can be had in a 2.0 or 1.5 Amp hour rating.
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Old 06-21-2018, 10:36 PM   #6
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What brand/model are they? Might be able to find a better source for the stats is we knew specifically what you are comparing.
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Old 06-21-2018, 10:37 PM   #7
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Originally Posted by Benthic2 View Post
the smaller one is 6.7 ounces and the larger one is 14.3 ounces

I would have thought the same thing..same volts, same AmpHours = Same watt hours.

I am about to buy 2 more and am wondering if I am just paying for a psychological factor of bigger size.

If we really wanted to complicate the issue...the larger battery comes in a 4.0 or a 6.0 Amp hour rating...and the smaller one can be had in a 2.0 or 1.5 Amp hour rating.
If you want to know what is inside, open it
I always did that with my toys lol

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Old 06-21-2018, 10:37 PM   #8
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These two batteries are exactly the same physical size, but one is a 3.0 AmpHour and 32 Watt hours.....and the other is 4.0 Amp hours, and 43 watt hours.


They are Milwaukee M12 Red Lithium Batteries
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Old 06-21-2018, 10:48 PM   #9
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I was/am mainly confused about the middle 2 that are both rated at 3.0 Amp-Hours...but here are the 4 that I own....The smaller size comes in 1.5 Amp hours...and the larger size also comes in 6.0 Amp hours.
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Old 06-21-2018, 10:55 PM   #10
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I was/am mainly confused about the middle 2 that are both rated at 3.0 Amp-Hours...but here are the 4 that I own....The smaller size comes in 1.5 Amp hours...and the larger size also comes in 6.0 Amp hours.
If they are all 12v maybe the manufacturer has a problem with maths
Beyond that, size factor is something, what is inside the plastic shell is something else.

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Old 06-21-2018, 11:34 PM   #11
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Likely slight differences that get rounded to a consumer friendly common number.
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Old 06-21-2018, 11:42 PM   #12
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There are cells in the same length with different capacities. If they are all from Milwaukee they are probably what they say. Aftermarket you can never be sure till you test them. I think the difference between the 32 and 36 WH is Milwaukee doesn't want to confuse consumers too much, with a 3.2 and a 2.7 etc. Nice even numbers.
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Old 06-22-2018, 01:00 AM   #13
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Please don't get me wrong...I have a bunch of tools in the 12 vold line and I love them all.....My preference is to keep everything 12
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Old 06-22-2018, 02:35 AM   #14
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They are not the same voltage. One is 12v 3.0 amp 36 Watts. The other is 10.7v 3.0 amp and 32 Watts. 10.7v is the original lithium ion spec. Later it was updated to 12v, the tools will run off of either voltage even the battery chargers will charge both batteries. 12v 3 amp 36w will produce more power or will last longer if loads are equal.
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Old 06-22-2018, 08:20 AM   #15
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Those batteries contain multiple Lithium ion 18650 cells. Those cells come in a wide range of amp-hr ratings ranging from about 1.5 to 3.5 per battery. The maximum discharge rate is also related to the capacity with lower amp-hr capacity cells generally having higher discharge amp-ratings (but not always). The nominal voltages on 18650 cells are 3.6 to 3.7 volts, but full charge is 4.1 to 4.2 volts. However most batteries limit full charge voltage to around 4-4.05 volts for safety and battery life reasons. Nominal voltage is normally used to calculate watt hours.


For a 12 volt battery pack there will normally be three 18650 cells wired in series. Voltage for series wired cells is additive so 3x3.7 = 12.1 volts and 3x3.6 = 11.8 volts. If they used 2 amp-hr cells the 3.7v nominal voltage cells would give a 2 amp-hr battery pack with a 24.2 watt-hr rating while 3.6 volt rated cells would give a 23.6 hr rating. Higher amp-hr batteries are normally built by having multiple groups of 3 18650 cells wired in parallel since amps are additive for parallel wired cells.


As far as the batteries in your picture go I would guess that they are built using slightly different capacity cells for the two 2 amp-hr batteries and that the 2 Ah rating is nominal. The higher amp-hr batteries have more groups of 3 series wired cells where the groups are wired in parallel to get higher amp-hrs.


Hope this helps.
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Old 06-22-2018, 10:19 AM   #16
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A bit of a drift but: I have found that rechargeable batteries that are not used regularly tend to die an early death. Replacing the batteries is often close to the price of a new tool with a new battery. Since I don't use my power tools very often (except for my Black and Decker cordless screw driver) I have begun using corded tools. It's a little hassle dealing with the extension cord etc. but the tool never disappoints and they are pretty powerful. Just sayin'
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Old 06-22-2018, 11:23 AM   #17
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A bit of a drift but: I have found that rechargeable batteries that are not used regularly tend to die an early death. Replacing the batteries is often close to the price of a new tool with a new battery. Since I don't use my power tools very often (except for my Black and Decker cordless screw driver) I have begun using corded tools. It's a little hassle dealing with the extension cord etc. but the tool never disappoints and they are pretty powerful. Just sayin'

That is true for the older battery tools that use Nickel metal hydride batteries. Newer tools with lithium batteries maintain charge much longer and don't have significant capacity loss over time or when left partially discharged.
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Old 06-22-2018, 07:39 PM   #18
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So after a little internet sleuthing I see you guys were right ( as I expected ) Both sizes of battery are just a case that holds 3 x 18650 batteries, so the shape/size is irrelevant and the differences are due to the varying capacities of the cells inside.

Thanks for all the feedback !!
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Old 06-22-2018, 10:55 PM   #19
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Originally Posted by hmason View Post
A bit of a drift but: I have found that rechargeable batteries that are not used regularly tend to die an early death. Replacing the batteries is often close to the price of a new tool with a new battery. Since I don't use my power tools very often (except for my Black and Decker cordless screw driver) I have begun using corded tools. It's a little hassle dealing with the extension cord etc. but the tool never disappoints and they are pretty powerful. Just sayin'
I totally agree.
I have one set of twin drill/driver RIGID from Home Depot. Came with 2 rechargeables and a charger. The driver has replaced so many ordinary screwdrivers, the drill actually works. They get enough use that the batteries are in great shape.
Other than that, all of my rechargeables got little enough use that they were throw-away tools when the batteries died, as the cost of new batteries was prohibitive.
I have only corded tools where real power is required.
A Milwaulkie 1.5 hp drill is the best drill I have ever used. When I have a BIG job it is my go to tool.
My Makita Skilsaw blows my RIDGID battery powered skilsaw totally away.

Sorry about continuing the drift.
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Old 06-23-2018, 12:39 AM   #20
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Both battery and motor technology have made huge strides in the last 5 years or so. A corded tool will almost always have more power, but for 95% of what most people do, todays cordless tools are more than enough. A lithium battery and a brushless motor make a big big difference. A lot of contractors I know are now using 12 volt instead of 18 or more. When you are using a tool all day long, a pound or two of weight makes a big difference in arm/hand fatigue.

My 12 v Milwaukee driver has no trouble driving 6 inch lag bolts (6" x 3/8") into pressure treated lumber without pre-drilling, and I've snapped a few #2 phillips driver tips with it.

If you are an infrequent tool user, a flashlight that runs off your drill battery is a great way to keep the batteries in use. Keeping the batteries charged helps prolong their life.
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