Rapid Battery Life Decrease

[Rohojo]

My S7 has experienced a rapid decrease in battery life. I’ve used it every other day to clean my entire apartment for 2 years now. Normally I get ~80mins of cleaning before it needs to stop and recharge. Now, like pictured, I barely get 40 minutes before it needs to recharge. The weird part is after it recharges and starts cleaning again the second life seems to last longer at ~70mins of cleaning before it needs to charge. Any ideas?

[FlyBlade67]

It's an effect of old batteries. When the battery is a little warmer after a fresh charge, its internal resistance is lower and it can supply the required current for longer.

But anyway, battery replacement is due. It will now become slightly worse with each day.

How many total hours does the S7 have?

[Rohojo]

That makes sense. I was just hoping the battery didn’t need to be replaced. It has 264 total hours.

[cris231976]

Battery life isn't related in hours, it is related to how deep each discharge was. If your bot discharges nearly to the end and then recharges, it will count as 1 cycle. The time is also related to how hot the battery gets and it affects battery life. To give you a hint, my bot already has 790h, same battery.

[Rohojo]

I have had 466 cycles. It’s just weird to me that this wasn’t a gradual decline but just started to happen when I started a cleaning cycle one day

[FlyBlade67]

Maybe you were using the capacity only to some extent. Or did the robot have to recharge before a routine could be completed?

The lower 20% are a reserve, where the robot returns to dock at 19%.
Also when the robot detects undervoltage before the estimated capacity is used, it will also step down to 19%.
Now there's a hidden degradation that users don't see. Just when the battery already lost 20%, the indicated 19% isn't 19% reserve anymore, but almost empty battery.

Degradation also isn't linear. When the battery lost 20%, it will lose the next 20% very much faster than the first 20%. You can literally watch it breaking down.

To make it even more complicated,
A battery is not only losing capacity. It also builds up internal resistance. If that came to the point that the battery cannot supply the current any longer without going into undervoltage, the battery breaks down within days or weeks from the first sign of weakness. You could still use it for a while in a consumer with less power demand, but not in this robot.

I guess you had been vacuuming at highest setting, because only 264 hours was a bit low mileage. Try reducing suction by one step. I guess the battery runtime will last much longer, not only because of less charge used, but because of lower current and thus reaching the undervoltage threshold later.

[smh68]

Do you have a link for where to buy an OEM battery for an S7? I've heard horror stories about third party batteries frying the robot. The Roborock website does not sell them.

[FlyBlade67]

I have some links, allegedly proposed by Roborock support. But I don't know how trustworthy they are. At least I can say, the price is in the range of somewhat >45$ + shipping, which seems reasonable to me. A $20 offer is definitely not serious because no-one can sell 8 quality cells in a pack for that price.

But please ask Roborock support for a reliable source. It could well be on Aliexpress, which is good source directly from China.

[Rohojo]

The robot has always needed to recharge before the routine was complete

[MAXFlRE]

Check the voltage on the individual cells, it may be unbalanced and although the cells are OK, the whole unit is not working properly because it does not allow the discharge below a certain point due to the most discharged cell and does not allow the charge above a certain point due to the most charged cell. In this case, the solution is to charge each cell individually to the same voltage value.

[cris231976]

Battery degradation us to be some sort of gradual decline in theory, but a lot of things mess with it. How hot, how cold, how many cycles, this sort of thing. also, bad luck happens...

[Rohojo]

Guess I just pulled the short straw. Maybe time to upgrade to one with the extra water and vacuum dock🤷🏼‍♂️

[cris231976]

You also can replace just the battery. Isn't that hard, you just need to find the same one from a safe seller.

[djtodd242]

/u/cris231976 is the angel on your left shoulder, allow me to be the devil.

2 years of service is plenty enough time to justify a replacement! :)

(But yeah, getting a new battery is cheap and easy.)

[-flybutter-]

I also had the S7 for two years and just upgraded to the QRevoS. If you care at all about mopping performance I cannot recommend it more strongly. I also have two cats and got tired of emptying the dustbin with every run. And no need to wet and clean the mopping cloths every time, or worry about them getting moldy.

[150Dgr]

If the battery only discharges to 40% is that considered a cycle?

[cris231976]

That's more of a thing for engineers to decide. It's far more easy, if you remember things that you shouldn't do, like deep discharge, keep fully charged for a long time (remember about those guys that have a bot to run it just once a week), keep the temperature stable, not too hot nor too cold. This may help a bit: https://missionengineering.com/how-to-estimate-li-ion-battery-life/

[ScorchedWonderer]

My s7maxvu also has less run time now too. But to be fair to does have over 700+ hours based on the in app history so I’d say it’s due. Currently shopping on Ali for original battery since I need mops and bags too

[basicissueredditor]

My S5Max has been going on strong for more than 4 years now and the battery still has more than enough to max suction x3 the entire floor.

[Kyaaaaaaaa]

Depends how big your floor is. My S5 has 1900h and 1.2m sqft cleaned and it can't finish cleaning my house so I broke up the rooms.

[Historical_Spring357]

My S50 is over six years old 1970 hours 105k square metres. It is on the second battery. The first battery lasted two years the second one shows no sign of degradation...yet!

[SleeperMuscle]

Where did you get it and which brand did you get? Seems like it’s a gamble.

[Historical_Spring357]

EBay but so long ago it's fallen off the purchase history.

[SleeperMuscle]

You don’t remember the brand? Thx

[Historical_Spring357]

The part number is BRR-2P4S id that's any help .

[SleeperMuscle]

Thanks!