# Bosch 43 LI Lawn Mower

How long does the team think the Bosch Li-ion batteries should last before failing. The unit in question has a 36v x 4Ah battery at ~£160 a pop.
There are two batteries, but only one is used at a time. Both batteries are not holding full capacity, with one being worse.
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Smolley wrote:

This site has some background info.
https://batteryuniversity.com/learn/article/charging_lithium_ion_batteries
Charging is pretty innocuous.
https://batteryuniversity.com/learn/article/how_to_prolong_lithium_based_batteries
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"Lithium-ion degradation at varying discharge rates"
https://www.sciencedirect.com/science/article/pii/S1876610218305915
"It is found that after 400 cycles the cells discharged at 1 C and 3 C have capacities of 83.9 % and 81.4 % respectively of the maximum capacity recorded."
That means the rate the battery discharges is slightly important.
Your battery is 36v x 4Ah
Discharging at 1C would be 4A or 144W.
Discharging at 3C would be 12A or 432W.
My line powered lawn mower advertises 1035W. And would only draw that current in heavy grass. Power drops when the motor is free-wheeling.
For your mower to match mine, it would discharge at 7C (if the motor has the range to do that).
If the battery pack gets too hot, the safety will likely cut it off.
And the controller in the mower also stops the mower when the batteries get too low. That helps prevent damage to the pack. You can't run them completely flat - not allowed. The controller will stop it.
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There is a tradeoff in construction, between the discharge rate allowed from the battery, and its total Ah rating. You could limit the battery to discharging 1 amp, then optimize the separator and plate construction for a higher resistance. The end result would be the battery could have a higher Ah rating. Maybe instead of 36V @ 4Ah it could be 36V @ 8Ah. The disadvantage is, the current flow rate available "won't cut the grass". This means not all the battery types on the market, are good enough to cut the grass.
https://www.grepow.com/page/high-discharge-battery.html
I found an article the other day, that compared various battery products available, and their max-discharge-rate versus their Ah-rate, and you can see the clever tradeoff between packs with low internal resistance, versus packs that have increased overall capacity.
And portable power tools should take some of these things into account, when they pick a cell sub-type for the job.
And that's not the limit on voltage. There is a snowblower product with dual 56V packs. Only one pack used at a time, like your lawn mower. The price of the packs would take your breath away. Probably twice as expensive as the one you got. You really have to wonder at the economics after a while. And the snowblower in this case, has gone from "completely unusable" as in previous years, to "can now handle a light snowfall". There's still no battery one that could hand 18" of snowfall. If you were in the snow belt here, you'd have to buy a *lot* of spare packs and the expensive pack chargers, so you could charge packs in parallel on a snowy day. You would have to go out once an hour, and remove the snow, so the buildup would not exceed device capacity.
My next door neighbor likes these battery gadgets, and he has to recharge his mower before he can do the back yard. It takes two charges to do the whole property. He threw away his previous battery mower after about four years usage. He's great with gas (can repair small gas engines like the breeze). His electrics just go into the skip when the red LED comes on... Seems uninterested in fixing.
A guy in a pickup truck stopped, when he saw that mower out for collection, and asked if he could have it. So some people know these can be fixed. You would need tabbed batteries and have a sense of adventure (in case one catches fire because of a mistake you made). Don't work in the house on stuff like that. Take it out to the patio.
The packaging of the battery packs is normally made in such a way as to discourage repair. That's the way it was in the NiCd era.
Paul
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It depends...
How many cycles do you reckon you've put on it? Are they likely to have been full-to-empty cycles, full-to-half, or what kind of usage?
What do you reckon is the current capacity? 90%, 80%, 50%, 20%?
How hot does the battery get in use?
How old is it? How many winters has it been laid up?
Theo
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wrote:

Does that matter? When citing the duty of a Li-ion battery, 500 cycles is sometimes given. Does charging a 50% depleted battery twice count as one cycle?
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Cheers, Rob

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wrote:

I think there are things that could matter on life expectancy (and therefore those sorts of stats could be relevant, looking at it at a more granular level), like, if the mower was kept on maintenance charge 24/7 and therefore the battery on 100% charge level, I believe that alone can have an impact on capacity and/or life span.
So, I believe the idea storage charge is around 40% of capacity but how would you judge that, unless there is some sort of charge state indicator on the system?
This is the *biggest* issue with electric stuff like power tools / mowers (not such an issue for those reasons with mobile phones that may not be left on full charge for any length of time (we know it doesn't do laptops any good)) and why some stick with petrol mowers as they generally take less in the way of winterisation or require large sums spent on them even if you don't use them (or especially if you either don't use them or use them lots).
We have a battery vacuum cleaner (well, we will again, when the one that daughter bought us, then borrowed, and has just replaced for us is delivered) and because that doesn't need laying up during the winter and is used reasonably regularly though a reasonable range of charges, doesn't suffer from those issues as such.
Maybe a battery cleaner (or power tools etc) kept at a summer only holiday home might need taking home and using sometimes to keep it at it's best?
Funnily, I pulled out an old battery drill that Dad used to keep down their static caravan and I can remember it being flat every time it was needed and quickly not lasting very long once charged. I've noticed it's 7.2V so I may well pull the cells out and add a 2m cable and with some Anderson powerpole connectors on the end that match all my good quality 7.2V RC car packs and then use it as semi-cordless. ;-)
Cheers, T i m
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It's all a bit handwaving, but charging 50% might count for half a cycle yes.
300-500 cycles is the spec-sheet number. I'm trying to work out whether the OP is in that ballpark, or miles away (if they did say 40 cycles I wouldn't expect it to be anywhere near losing capacity).

That's the tricky thing. If the charger was smart you could put it in storage mode at the start of the winter - but then the charger would need a resistor and cooling to dump excess energy and they don't want to pay for that.

I'm curious about this because I recently bought a used cordless vacuum. It has an aftermarket battery in it, and when run in 'Max' mode the battery gets quite warm, and then you put it on charge while hot. I'm wondering whether battery heating is the reason people complain their vacuums need new batteries, or whether they actually go through the rated cell cycle life of 300-500 cycles.

This is one advantage of battery-sharing systems. You can take the batteries out and use them in something else during the winter.

A similar thought went through my mind when I recently dumped a NiCd cordless drill. Although a) it was knackered and b) motors have got a lot better in the last 15 years. My £25 Aldi replacement is miles better in every way...
Theo
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On 15 Jul 2020 15:54:42 +0100 (BST), Theo

Quite.

Half cycle of the allowable DOD, depending on how the BMS is set. ;-)

As you say, unless someone keeps a pretty good log (or it's built into the BMS) it's all a bit finger in the air.

Agreed.

Indeed. That's why I wondered if the mower / battery had any sort of charge status indicator in which case you could keep mowing (or stop mowing) when it shows roughly half full on the last mow of the season. ;-)

Good point. I have a Samsung Galaxy S7 that I had soon after they first came out and have used every day since then. I normally put it on charge in the evening (and take it up to bed in case of emergencies) and might put it on charge again in the morning if I know we will be out most of the day. Some years later it seems like it's loosing capacity (it might run out by the end of the day) but considering how many cycles it must have done, I think it's done pretty well. Part of that might be that even though it supports smart / fast charging, I've kept it on a std / slow charger for the exact reason you suggest, keeping the battery cool. I can also tell if the GPS has been turned on in use but how warm it feels.

Agreed. My FatMax drill has two batteries and daughters Lidl drill, jigsaw and circular saw have 3 between them so you can share the load / charge / cycles.

I've done it previously with a 'big' cordless drill that I bought pretty cheap from the market (I know the guy and he rated the motors and gearboxes etc). Being Nicad they have eventually failed so I've emptied one battery (it came with two, both have failed for lack of use) and I've just fitted a heavy duty twin core / sheathed cable with some crock clips on the end. Not short of all sorts of 12V power sources here so as ling as I'm not moving around too much, it's not really an issue. ;-)

Well there is that, however, it's also nice to be able to leave bits in various drills to cover the range of things you are doing (pilot, clearance, countersink, driver).
Thinking of my RC car racing days ... even then some of the chargers came with fans and cradles built in so the battery sat if fresh moving air as it was being charged or cooling after a race.
Cheers, T i m
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Those gauges are often based on battery voltage. It's easy to work out the start and the end of the discharge curve, but the part in the middle is mostly flat. If 80% is 3.78v, 50% is 3.72v and 20% is 3.68v (completely made up numbers) it wouldn't take much for a voltage-based gauge to be way out.
Every tool I have that I've opened has two wires going to the battery gauge, which means it's just a voltage measurement rather than a watt-counter. (Possibly fancier Makita/etc do it better)

Mobile batteries are slightly different in that the charge/discharge profiles are relatively small. You might have say C:h and the discharge current might be C or C/2. If you have a drill or saw with C:h the discharge current might be 5C or 10C. The battery works a lot harder and gets hotter - in a phone generally the battery doesn't get hot of itself, it's just by being next to hot things.

For this reason I bought two Aldi £25 drills :) It was cheaper to buy another drill than a second battery. Back then they didn't have the interchangeable battery system - and of course that means you have to buy all your tools from Aldi...
(Should I mention the four Lidl pruning saws I bought for the same reason ;-)

I think some battery chemistries can deliver more current when warm - so you win the race if your battery is fresh off the charger. I think that applies to lithium ion too.
Theo
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On 15 Jul 2020 21:40:35 +0100 (BST), Theo

Agreed. However, I have some experience with the battery gauges on disability scooters and the ones I've played with seem to have a fairly representative charge indicator?
Start off on 5 bars, soon drop to 4, slowly go though 3, 2 and 1 and then it stops. ;-)

Understood.

<snip> >

Ok.

Nope, I can assure you that I can tell when the GPS is on on my phone by how warm it is. ;-)
Under normal circumstances (even when charging on the slow charge) it feels cold to the touch.

Yeah, you often see that. Or get extra batteries 'included' for way less than you would buy them for separately. The last time I did that was with an RC Drone. ;-)

Crafty.

Hehe. Plus you have plenty of spares. ;-)

Sure, as long as they don't end up too warm etc.

I think most everyday battery suppliers / chemistries suggest an ideal working temperature range. Lead acid (capacity) certainly suffer quite a bit when cold.
Cars that won't start first thing in the morning but will later on when it warms up a bit. ;-)
Cheers, T i m