What does the 56 Volts of your batteries tell me about them?

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I am researching battery powered OPE for the first time and looking at the various brands that are available.  It seems that the various companies all list different specifications for their batteries.  What does the voltage tell you about the end use of the battery? Does it mean that the battery will last longer, can deliver power to the motor more quickly, etc?  My experience with cordless hand tools is that just because a particular tool is say 24 volts does not mean that it is more powerful or stronger than a 18 volt tool.
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Posted 4 years ago

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Tarheel, you've got some great questions.

To start off, probably the most important factor in a battery pack is its capacity.  In small batteries this is usually referred to in Watt-Hours (Wh), and in larger batteries, like those in electric cars, in Kilo-Watt-Hours (kWh).  1 kWh = 1000 Wh

To determine the capacity of a battery pack you multiply the Voltage (V) and the Amp-Hour (Ah) rating.  Example, a 2Ah 56V Ego pack has a rated capacity of 112 Wh (56V x 2Ah).  The capacity in Wh tells you how much energy is in the pack.  The more energy in the pack, the more work it can theoretically do on a charge.

You can juggle those numbers around a bit and see that a 28V 4Ah pack would have the same capacity as a 56V 2Ah pack.  Same goes for a 112V 1Ah pack.

Higher voltage systems do carry an advantage, though with small increases in voltage that advantage is slight.  Generally speaking, for a given amount of power output, if we increase the voltage the current requirement goes down.  Primarily, this allows for smaller gauge wiring and is the main reason why power transmission lines run at very high voltages... less current allows for thinner wires.

In a power tool application it's not quite that simple, and I'm far from qualified to comment on electric circuit and/or motor design.

Going back to pack capacity, let's compare a few common packs:

56V 2Ah = 112 Wh (Ego)
56V 2.5Ah = 140 Wh (Ego)
80V 2Ah = 160 Wh (Kobalt/Greenworks)
40V 4Ah = 160 Wh (DeWalt)
58V 4Ah = 224 Wh*** (Echo)
56V 4Ah = 224 Wh (Ego)
40V 6Ah = 240 Wh (DeWalt)
56V 5Ah = 280 Wh (Ego)
56V 7.5Ah = 420 Wh (Ego)

(All packs rated using 4V/cell to keep things equal.  Actual rated capacity varies slightly)
*** Echo 58V packs use 14 cells in parallel, their marketing team added 2V.

As to your comment regarding current draw vs. capacity, you have an excellent point!  Just because it says it has more voltage doesn't mean it has more power, absolutely true.

When I started looking at battery powered OPE, I discovered Ego's fan cooled battery charging system and their phase-change cell wraps.  This is, as far as I'm concerned, the only battery system designed PROPERLY to handle the rigors of the constant drain applications of Outdoor Power Equipment.

In a nutshell, as a battery heats up under load its ability to maintain both its power output and its capacity diminishes.  I know this from being a bit of a battery geek for a while, and if you want more detail you can watch this guy's teardown video that shows the difference between the Ego and Echo batteries:


He has another video that really drives home the importance of keeping the batteries cool.  He operates the Ego and Echo blowers wide open and then takes the batteries out of the blowers and immediately recharges them, over and over, to see how much work each battery platform can actually do over time:


To me, that one really shows off the Ego's design advantage.  As is pointed out in the video, all the other companies seem to just put a bunch of batteries in a box and call it a day.  Ego is the only one who have seemed to take care of keeping the cells cool and operating within a designed temperature range.  Since high temperatures reduce lithium cell capacity and lifetime, this seems like a smart way to go.

He also has a video demonstrating the difference in charge times:


Keeping things cool allows you to charge the packs MUCH quicker without hurting the cells.

This also holds true when discharging the packs.  Since the Ego packs will hold their cells at a much more consistent temperature, their performance under load should be better, while reducing the risk of thermal overload as well as heat related wear on the cells.  I can cut my lawn with the 20" mower using the small 2Ah battery, and the pack is barely even warm to the touch when I take it out.

Having said that, and to elaborate on your question a little, the mower WILL struggle a bit more through heavy grass when using the 2Ah battery.  If the grass is really thick and/or tall, the 4Ah battery will allow the mower to power through it with less slowing down.  The 4Ah pack has TWICE as many cells to draw power from, so the load per cell is reduced dramatically.

I hope that helps explain a few things, including why I chose Ego OPE when deciding I'd had enough of dragging cords around my yard!