Robotic lawnmowers - anybody tried one?

I wonder if it worth taking it back as Ryobi has a 3 year manufacturer’s replacement warranty.

In theory, a 5Ah should last about twice a 2.5Ah operating under the same conditions.

As its capacity is not fully discharging, it looks like it may have a fault either with one of the cells or the circuitry.

Have you tried allowing the battery to fully cool to see if the fault is overheating of the discharging cells. If it discharges full when cooled, it could be also be a temperature sensor issue/fault.

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I actually dug out the receipt for the battery on the weekend, but I need to check whether that 3 year warranty is retrospective - I fear it’s not.
The battery doesn’t get warm like the 2.5Ah one does after use, but even so, if I leave it for an hour or so it still won’t power the mower. I’ve seen other negative reviews for the 5Ah batteries, so perhaps the early ones were simply not up to scratch for whatever reason.
I also haven’t come across any 9Ah battery yet.

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The good news is that the battery is covered. The bad news is that there are no replacements in stock at any of the local Bunnings stores.

I also got a strange runaround from staff - the Returns desk called over someone from Power Tools who said that it wasn’t their responsibility, and handed me back to the Returns desk, telling them to call Garden Tools. After a wait, someone from Garden Tools came down and did a stock check, but then informed me that it would need to be dealt with by somebody in Power Tools, and as he was not rostered on until the afternoon, I’d have to wait for him to call me… Seems a shame that the Returns desk can’t actually handle returns !

I was told that the 5Ah model has been replaced with a newer version. I’ll let you know what it’s like when/if I get hold of one.

To return to the thread topic, it got me thinking that not only is a robot mower an attraction to thieves, but also the no-doubt-expensive battery.

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Hello all, I have just been reviewing these threads, and I think that I can offer some expertise on the subject of robot lawn mowers, as we are an Australian brand for these devices. I am not seeking to promote our own brand here, you can make your own choices. I will try to answer any questions that people have, as objectively as possible, but will not tolerate any abuse, and will ignore any sarchasm or cynicism, as this tends to come from people who think they know better. Going through the points observed:
1. History
Patents for robotic mowers can be found back as far as the 1970’s. But they weren’t really developed until the mid 1990’s, and Husqvarna was at the forefront of this. Commercialisation didn’t really start until the mid 2000’s, and sales didn’t take off in Europe until after 2010. Between 2010 and 2019, Husqvarna themselves for example had sold more than 1.5 million robotic mowers in Europe, and the market segment was a key contributor to their bottom line.
2. Brands
Did you know that Husqvarna own 4 brands in this space? Husqvarna, McCulloch, Flymo, and Gardena. Yes, the device you see in Bunnings is Husqvarna’s ‘budget’ brand. The Ambrogio brand is not Australian, it is Italian. There has been one Australian builder that has developed a robot mower, Elite Robotics, based in Newcastle, but I’m not sure if this is available commercially, and even if it was, whether or not it would be competitively priced. You can look them up.
3. Edges
Yes, getting the edge cut is the challenge for these devices. Most models rely on a boundary wire signal which defines the cutting area, and it is a skill to get the wire as close to the garden edge as possible, without the mower getting stuck on walls, garden beds, etc… Worx has models which claim to solve this, but I’m not able to validate how well it goes. Perhaps someone else with experience can comment.
4. Quality of cut
In my personal experience, the robotic mowers give an excellent quality of cut. Especially if the blades are sharp. As with any mower, it is useful for the blades to be sharp. The type of grass doesn’t matter, they will negotiate all kinds, but don’t expect a robot mower to perform well if the grass is a foot long. I have not seen any evidence of disease spread, or dead patches of lawn. Also when I compare areas where the robot is used adjacent to where the robot is not used, the grass doesn’t seem to grow as fast. Not sure why. The robot mowers do not collect grass, but leave it on the lawn to be mulched. It is said that when this is done, the lawn should be ‘thatched’ every few years, but we’ve not had to do that yet. The robots will cut wet grass. The issue with cutting in the rain is more about the wheels losing traction on a slippery surface, especially on a slope. For this reason, most models have a rain detector thaw will make them return to their base station.
5. Size of lawn
Size matters when making your choice. You may find that a mower designed for small areas is priced as high as other mowers for large areas. Most backyard lawns are small - you would not choose a ride-on for that job. And a 1hp push mower would not be suitable for a 1 acre (3400sqm) paddock. As with anything, it is important to choose the tool that is fit for purpose to the task. And the battery is all important in this respect as well.
6. Batteries
Most robot mowers will be about 24 volts (avg., 29.4 peak). Batteries can come in sizes like 2.2Ah, 4.4Ah, 6.6Ah, 13.2Ah. The smallest size will drive a small mower for about 45 minutes and be suitable for lawns up to about 800sqm, give or take. The largest size will drive a large mower for up to 4 hours, and be suitable for areas up to an acre (or more). The bigger the battery, the longer it will take to recharge. Lithium batteries require care, and should be recharged regularly. If they are stored flat for long periods, they can become irreparably damaged.

I hope these brief points help, I could offer feedback on other points, eg safety, programmability, versatility etc., but none of these other points were raised in the thread

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Welcome to the Community @robotzoo,

The Community welcomes expert information from all members, including business people. Thanks for posting - very informative - and well done for identifying your interests.

It would be appropriate if you filled in your profile to avoid needing to include your business relationship in future.

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I completely forgot to come back with an update on the Ryobi 5Ah battery. It seems just fine after a year or so of use. It certainly gives the mower plenty of runtime - sometimes sufficient to do both front and back lawns, and also seems to have better voltage output than the lesser capacity battery I have ( although to be fair, that battery is quite a bit older - maybe I’ve forgotten how good it was back when it was new ).

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Hi, a bit of what I know about rechargeable lithium batteries…
Most rechargeable battery packs are made up of standard 18650 cells, which look like an oversize AA cell. Even a Tesla uses these! The individual cells could be from 2200mAh to 3600mA. They are rated at around 3.675V (peak, 3V avg.), so when wired as a bank in series you get a multiple of this eg. 14.7V (12V), 29.4V (24V). etc… The banks can then be wired in parallel to give 4400mAh, 6600mAh etc.
Having a larger bank (or number of them) means the battery pack is less susceptible to the failure of any individual cell, which can happen as a chemical reaction if the charge is allowed to fall below a certain threshold level (according to the specs of the cell). That’s why some packs will never be able to be recharged back to their original spec. It’s also why a 5Ah battery will always be a better choice than a 2.5Ah battery, because there is some redundancy there, notwithstanding the extra Ah.
18650 cells are supposedly good for between 300 to 500 ‘cycles’. That is why it’s recommended that you use the pack until it goes ‘flat’, before recharging, to get the most out of the battery life.
Battery packs will also have a battery management system BMS circuit board which will govern when the pack should stop discharging (when low) or stop accepting charge (when high), to protect the cells. We have found that sometimes it is the BMS that fails, not the cells, ie. the pack shows low voltage & won’t accept any charge, but when you take the pack apart, all the cells are fine.

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Hope you don’t mind some alternate content.

There are numerous recommendations against this practice for the most common lithium battery technologies. Higher charging temperatures also have an adverse effect on battery life. The optimum total life of a lithium battery is achieved by recharging the battery before it is 50% discharged.

The following relates some relevant battery test results.

Under test common NMC lithium batteries delivered 300 cycles at 100% dod (depth of discharge) or 1000 at 40% dod. Approx 30% greater lifetime capacity with more frequent recharging.

LiPO4 batteries delivered 600 cycles at 100% dod or 3000 at 40% dod. Approx 2 times greater lifetime capacity with more frequent recharging.

Doesn’t reliability analysis predict the more cells in a battery bank, the more likely a pack will fail?

When a single cell in a bank in series fails early how does that bank continue to function? Or does the built in protection create an open circuit for safety?

For multiple battery banks in parallel when a cell in one bank fails, does that reduce the battery capacity by 50% if there are two banks; less so by 33% if there are three etc?

This would suggest a higher capacity battery with multiple banks of cells is not necessarily better value. They are more likely to fail and loose a large portion of the capacity when just one cell fails early.

Note:
Domestic use products that use replaceable lithium battery packs are now providing for warranties of 2-3 years on the batteries.

The fine print and ease of obtaining warranty (retail and statutory warranties) might be far more relevant to a purchase decision.

P.S.
The more frequent recharging strategy at around 50% charge remaining also works great for mobile devices, giving up to twice the total lifetime use.

Sorry the brevity of my post may have been a bit misleading. All my comments about batteries are based on our experience with using them on robotic devices, not so much about empirical research. When I talk about running the battery pack ‘flat’, it means as low as the BMS will permit, which for any 3.65V 18650 cell would not be lower than about 2.7V, because this is the threshold below which the chemical reactions can occur to degrade the battery cell. So yes it is not good to discharge the cell below 50%.


Regarding LiPO batteries, these are the ones that are usually encased in a soft, malleable, polymer pouch casing, and will be used where light weight and high energy density are important. They can still be wired in ‘banks’, with a BMS. We find they don’t perform nearly as well as what’s stated, and when they ‘swell’, you know they’re gone.

Take for example a 29.4V battery pack that may contain 3 banks (connected in parallel) each of 8 2200mAh cells (connected in series)… did I get this wrong in my previous post? … to deliver 6.6Ah

Regarding the failure of cells, it could be the cell itself, or the wiring connection to the BMS, or the circuitry of the BMS monitoring/controlling that cell. But the pack when faulty will not charge more than a certain voltage. It could be around 24volts, 18 volts, or even as low as 3.6 volts (ie. equivalent to just one good cell in one of the banks). So I expect that the whole pack will only charge to a voltage which is the limit at which the most faulty bank will charge.

Regarding mobile batteries, they are usually a single 3.8

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