Freezing Batteries to Reduce Overload

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I am having problems with the mower shutting off due to overload again in the thick patches in my back yard.  I have gotten used to it, but my new neighbor was really interested in the Ego mower (he was using a reel mower) until he saw it shutting off for 5 minutes after every minute or so of mowing.

I could write the book on maximizing battery life and performance, sharpening the blade every mow, mowing dry lawn twice per week, graphite coating on perfectly smooth underside of deck, etc.  I have also figured out that swapping batteries seems to make the mower recover faster and run longer before overloading again. 

Since both batteries were fully charged, and I noticed they come out of the mower much hotter than usual, I decided to stick the other one in the freezer when not in the mower as I swapped them out.  5 minutes in the freezer doesn't even get a hot battery down to room temperature, but much cooler than sitting in a 95 degree garage.  Cooling the battery for a few minutes doesn't keep the mower from overloading, but it does keep it working between shutoffs for a few precious seconds longer.

So, if a little cold is good, is a lot better?  Could I stick my fully charged batteries in the freezer overnight before mowing the next day, putting an ice cold battery in the mower instead of room temperature?  I don't know a lot about battery cells, but I do know that heat is bad so it seems like cold would help extend life and run time, as well as reducing overload shutoffs.
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David Cline

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Posted 4 years ago

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SCDC, Champion

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Hi Big Dave,

You took me down memory lane, when I was a kid, the engineers stored all of their batteries, from flash light batteries on up in their fridge. 

My batteries are getting a bit more heated than last year, but it's 10 degrees warmer outside than last year, it's just plain brutal!  I wonder if a small vend/fan inside the battery compartment of the mower would be helpful.  Not an unreliable circular fan, but one of those blower types.  They never burn out, use next to nothing with current and move a lot of air.

(Edited)
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Blue Angel, Champion

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Official Response
David, most freezers would chill the Ego batteries well below the point of optimum performance.

However, a refrigerator usually stays a few degrees above freezing which is well within the operating range of the battery. Sticking your fully charged packs in the fridge over night might get you a little bit more mowing time before the cells get hot.

Do keep in mind, the mower has its own overload protection that will intervene regardless of battery temperature.
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David Cline

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Thanks for the heads up about the operating temperature!  I also found this in the manual:
COLD WEATHER OPERATION
This Lithium-Ion battery pack will provide optimal performance in temperatures between 32°F (0°C) and 104°F (40°C). When the battery pack is very cold, it may “pulse” for the first minute of use to warm itself. Put the battery pack on a tool and use the tool in a light application. After about a minute, the battery pack will have warmed itself and will operate normally.

As for the overload protection being activated, I assume this is due to a combined effect of a hot battery generating heat as it discharges while powering a hot motor that is generating heat due to the resistance, all in a hot environment.  Sort of a superfecta of heat. 

I have done as much as I can to reduce resistance, and can't control the environmental temperature.  I can't fit the mower in my freezer, so the battery is the only other factor I can control.  But a cold battery should help to cool the air around the motor and the motor itself through direct contact.
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Robert

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Another Idea to help keep the battery cool is to increase the air quality in the battery housing. There are no vent slats for the battery housing. Is this an oversight? 
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Blue Angel, Champion

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I believe this is done to minimize the amount of dirt and debris in the battery compartment.

There surely could be fresh air drawn through it, but it would need to be filtered in order to keep dust out.

None of the Ego tools are designed to draw air through the batteries while in use, though the other tools do leave the battery exposed to fresh air..
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Ken, Champion

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As a former professional photographer who had to baby rechargeable batteries NiCad and NiMH mostly) in some pretty brutal situations, I concur that refrigerator would be better than freezer.

It hasn't been hot enough this summer where I live for overheating to be a problem, but to SCDC's point, I often wonder whether simply removing the green plastic cover over the battery compartment would be a good idea on hot days to allow more air to circulate around the battery.
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SCDC, Champion

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That's not really a bad idea, but the amount of dust in the air when I mow, I can see it being an issue.  It isn't really that air tight, so I don't think the temps would improve much.  When I rinse off my mower, I do see some moisture in the battery compartment which I wipe out and keep the plastic door open to make sure it's dry.  I also spray the contacts with De-Oxit.
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David Cline

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UPDATE: 

Instead of continuously swapping batteries to cut one pass at a time between overloads, I fully charged the 4Ah battery and put it in the freezer for three hours.  (This was before I realized 32 degrees is the minimum operating temp, but did not experience any pulsating as described in the manual so may not have gotten core temp down below freezing.)

I resumed mowing where I left off with nothing else changed, and finished the rest of my back yard and all of my front yard on a single charge without a single overload shutoff.
(Edited)
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Blue Angel, Champion

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Good job, David! Next time try the fridge over night and let us know!
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bloomz

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Did nothing for mine - my first one - I'm on #3
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Ken, Champion

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Of course the question now is, how long will wives put up with us keeping our big lawn mower batteries in the freezer!
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SCDC, Champion

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My wife's sewing room has turned into battery charge and storage central.  I'm already on "thin ice".  David, I'm curious if the 7.5ah battery would solve all of your problem.  I'm in just about the same boat as you.  It takes about 1 1/4 charges to do my lawn.  A 7.5ah battery, I could do my lawn, use my blower and weed eater, and have time to eat lunch.  For those of you who can afford to get it.   My envy and jealousy will be quite obvious.  :/
(Edited)
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Paul

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Frankly this seems like a terrible idea, and a good way to void your warranty!

If my lawn caused the thing to overheat every few minutes I would call it a day and return it. I have pretty dense grass and have it turn yellow every once and a while, but if you are getting so many overloads I would raise your deck height to max, check for debris/sharpen. Maybe you have defective battery?
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Blue Angel, Champion

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A deep freezer definitely pushes things out of the recommended battery temps, but a refrigerator is generally several degrees above freezing. No problem! :-)
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David Cline

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Our fridge is 34... takes forever to thaw food, but the perfect temp for beer and batteries!
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Blue Angel, Champion

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SCDC, I think you have a point. With 50% more cells to absorb and dissipate heat, the 7.5Ah battery might help out immensely.

However, refrigerating batteries has a cool factor to it. :-)
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SCDC, Champion

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I still catch myself throwing my box of AA and AAA batteries in the side bin of the fridge.  The science is sound what cool temperatures do to atoms/electrons.  Everything slows down.  In fact, my PC's years ago, I use to use cooling systems to keep the CPU below 0 so I could clock to over 5Ghz.  Really helps with the things I do.
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David Cline

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Battery fridge!

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Rob

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Dave, it's great that you've been working with this problem but my question is:  Why haven't you bothered trying to get the problem item fixed under warranty?  Is there more to this story that I don't know?

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David Cline

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I don't think there is any defect with the mower or batteries.

The people who lived here before us had several bare spots in the sod from their dog(s) and must have seeded them with some kind of extra tough grass. All I know is that it has almost completely taken over the fine soft Bermuda sod and replaced it with this thick, coarse, possibly metal-reinforced grass.
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Dominic49

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the 7.5ah should solve your problem by virtue of having more amps available at any given time so as to not have the motor bog down.
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Eric

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I think you're confused on how volts/amps work on something like this.  They aren't changing the voltage, just putting in layman's terms "bigger batteries" in.  This will not produce any more power or reduce heat, it will only provide longer runtime.
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Blue Angel, Champion

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Eric, you're right, but it would seem the issue David is reporting seems to be related to heat buildup in the battery.  If this is the case the 7.5Ah pack has 50% more cells to share the heat load and should therefore heat up much less.

I see what you're saying in relation to Dominic's comment, in that the power of the system is determined by the tool, not the battery.  The tools can only draw so much power before they go into protection mode (overload).
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David Cline

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So does the capacity of the cells have anything to do with how much heat is generated as they are discharged? In other words, would the 5.0Ah fair any better than the 4.0Ah battery? I tend to think not.

Still, I think the bigger issue is the starting temperature of ~90 degrees, not the heat produced during use.
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Blue Angel, Champion

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Cells with a lower internal resistance will generally heat up less for a given discharge current.  I'm not sure if a higher capacity cell automatically means less internal resistance... I don't think so.  It's probably a case-by-case scenario based on individual cell model performance.

Then there's the cell performance at different discharge rates.  Power tools generally use cells that are considered "high discharge" designs, meaning they favor performance at high discharge rates over ultimate rated capacity.

High capacity 18650 cells (3Ah+) are very common and work very well in low discharge applications.  They rarely perform well in high discharge applications, which is why power tools have tended to rely on lower capacity high discharge cells.  Until a couple years ago these were pretty much limited to 1.5Ah capacity, hence all of the 1.5Ah and 3.0Ah power tool batteries.

More recently 2.0Ah high drain cells have been more common, hence the 2.0Ah and 4.0Ah power tool batteries.  Now we have 2.5Ah high drain cells available, and our 2.0Ah and 4.0Ah batteries are being upgraded to 2.5Ah and 5.0Ah models (and 7.5Ah in the case of Ego's BA4200 which uses three strings of cells).

In a few years we'll see the adoption of 3.0Ah high drain cells, and 3.0Ah and 6.0Ah packs (and maybe a 9.0Ah BA4200 replacement).  In a few years we are also expecting new battery technologies start production, so anything is possible at that point.

Exciting times to be a geek! :-)
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Dominic49

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Eric, I'm referring to the voltage drop that would occur as you are reaching the load limit. (yes I know its making a big assumption not knowing the C-Rate, but the available amps will typically will be greater in a higher watt hour battery pack)
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Blue Angel, Champion

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Another thought regarding heat in the batteries.  I have a relatively easy lawn to cut from a grass thickness standpoint, so my batteries are never even warm to the touch when I pull them out after cutting.

When I say that, however, I must add that the packs are never warm where it counts; that is, they are cool to the touch down on the body and in the center of the pack where the terminals are.  If the battery cells were getting hot this is where you would feel the heat.

I HAVE noticed that, when cutting the grass under bright sunny skies, that the TOP of the battery pack is quite warm.  I believe this is due to the sun heating the black rubber battery cap and the lack of ventilation in the battery compartment.

I have wondered if putting a reflective "shield" under the battery compartment lid would help keep the top of the battery cooler while cutting.  The issue I see with this is it would keep you from seeing the status light on the battery, but since the mower has its own status lights I don't see this being an issue.
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SCDC, Champion

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I've never liked dark colored ANYTHING when exposed to the sun.  It gets hot, fades, degrades, etc, so much faster than light colors or white.  Though white may not look pretty, it would cut down on quite a bit of heat for sun exposed surfaces.
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Tim1951

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I think there is something else at play here with your mower. I also have a very think patch of grass in my backyard and just finished cutting the lawn. Living in the Houston area, the temperature right now is 87 but feels like 95 with the humidity being 65%.. When I took the battery out to recharge for next time, it wasn't even really warm. The only things I do that may be different than what you do when mowing is that I bag instead of mulch and when I do the thick grass I do it in half passes so there isn't so much strain on the motor. I have never had the mower shut down.
(Edited)
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David Cline

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Bagging instead of mulching makes a HUGE difference. Narrower passes also help, but I prefer the appearance of full width strips.

I think it's worth noting that I found by the end of last summer that keeping a sharp blade and clean deck allowed me to cut my entire yard without a single overload shutoff. That continued to work until last week. The only thing that has changed is about a 10 degree temperature increase, from mid-80s to mid-90s.

That is why I think the primary issue is the battery temperature, not heat produced during use. Certainly some heat is generated, but it doesn't seem to be a problem if the battery isn't already pretty hot before even starting to mow.
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SCDC, Champion

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You also like a striping kit, so do I.  I miss that look!
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Tim1951

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With two dogs running in and out bagging is the only way to go for me.
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Jennifer VandeWater, Community Manager

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We do not recommend that you store your batteries in a freezer! Optimal temperatures are between 32°F (0°C) and 104°F(40°C). If your mower is truly “shutting off for 5 minutes after every minute or so of mowing,” that  is not right and we want to talk to you and see what is going on. Please call us at 1-855-EGO-5656 (1-855-346-5656) 8:30am – 8:00pm EST (Monday – Friday) & 10:00AM - 6:00PM EST (Saturday and Sunday) so we can solve this problem.

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David Cline

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Here is a video of me cutting the same amount of growth on the same exact strip of grass where it was overloading and shutting off constantly last week.  Same blade, same conditions, nothing changed except 20 degrees cooler today.  Not so much as a single flash of orange, much less any of the constant overload protection shutting off!



Clearly the ambient temperature of the battery is the issue, not the amount of heat generated by the battery or motor during use.  So starting with cool (but not frozen) batteries on excessively hot days should solve this problem going forward.  Storing them inside the house after charging might even be enough to solve the problem.
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Rob

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Question if you don't mind....Why do you not let customer service help you?  There really appears to be some sort of problem with your mower/battery. 

It's your equipment but I would think you would want to try to fix the problem if there is one.

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Blue Angel, Champion

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You may be right, David. If it's 90-something in your garage and 70-something in your house, you're giving the battery a 20 degree head start.
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SCDC, Champion

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I'm sort of with Rob on this one.  The mower and battery is more robust than what you are experiencing.  Seems like it is time for servicing.
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David Cline

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Well since the video never decided to work...


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David Cline

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Rob, I emailed support to verify that there is nothing wrong with my equipment.  I am 99% sure this is not a failure, just a limitation of operating in extreme temperatures.  I will report back if I learn otherwise.
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SCDC, Champion

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David,

We keep our house at 74 in the summer and 70 in the winter.  My batteries are stored in the house.  You should not be having that issue.  I would love to have some time with a 7.5ah batter to see if the mower reacts differently to what would be "trigger" events.
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Tim1951

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I keep my batteries in the house between uses as well and haven't had any issues whatsoever.
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SCDC, Champion

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Right on Tim.