You can set it in the BIOS menu. If you have Dell Command | Power Manager installed, you can also change this on-the-fly . For example, you can mostly have it set to charge to max 80% and start charging at 70%, for long battery lifetime, but change it to 100% when you know in advance you will need full battery.

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@sivanbh wrote:
Thanks for the reply. That much I know, what I'm looking for is to disable charging, rather than set percentages, some sort of toggle which disables charging until further notice. Alternatively, if I can disable charging through USB-C altogether, that will also be great.

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I don't think you'd want to do this, although building off the previous reply, I'm not sure why you'd want to.  If your system isn't charging, it will "self-discharge" over a period of time.  Batteries don't just hold their state of charge long-term on their own.  That's why the percentage system is used. It allows you to limit charging to a certain level (max charge percentage) and you can optionally ALSO specify a minimum charging level.  If you do that, then charging will be disabled on the laptop until it self-discharges to that level.  I've used this on my system for years and it works fine.  I'm not sure why having to manually manage charging would be considered preferable.

I'll refer to 2 different options that I'm looking for separately:

1. Toggle charging manually: before using the docking station, whenever I wanted to charge my battery I would plug the AC cable, and when I thought it's charged enough, I'd unplug it. If I know I need to have a full battery, I'd unplug later than normal. This decision making and manually plugging-unplugging the cable is the same as toggling manually. That's what I'm used to and it's the most flexible option. But I'd like to be able to do this while keeping the docking station plugged in (as it has a monitor and speakers, etc. connected to it), which is why I'm looking for a way to do this without actually unplugging anything.

2. Disabling the charging from USB-C completely: of course I know a battery will discharge without charging it (silly sentence). But I have a standard AC cable that I can use for charging. Like I wrote above, I want to keep the docking station connected at all times, but I want to control charging manually. So if I can prevent it from ever charging through USB-C, and just use the cable like I used to, then problem solved.

I have an XPS 13 9350 right here.  It's running BIOS 1.7.0, and if I go into the BIOS Setup, expand Power Management, and select "Primary Battery Charge Configuration", then select Custom, I can specify custom charge start and stop percentages.  I'm not sure why you wouldn't be seeing that on your own system or why Dell Power Manager isn't working.

As for the "silly sentence", you may not have understood the distinction I was trying to make between discharging and "self-discharging", because the percentage option offers a capability that is far superior in terms of battery longevity compared to your manual solution of just connecting and disconnecting the AC adapter periodically.

Discharging is when your system is actually using battery power to run itself.  "Self-discharging" is when your system is connected to AC power and is using that AC power to run itself, but is NOT doing anything with the battery, i.e. it is neither charging the battery nor drawing from it.  It's equivalent to running the system on AC power with the battery physically disconnected.  In that state, the battery will still discharge slowly over time simply due to chemistry, even though there's no active load on it -- hence the term "self-discharge".  That option of being able to have the system run on AC power while leaving the battery essentially disconnected is far better than your manual method of connecting and disconnecting the AC adapter periodically, because that manual solution is putting a bunch of additional unnecessary cycles on your battery by forcing it to always be either charging or discharging.  You're right that keeping a battery constantly topped up isn't ideal, but it's still better than several extra cycles, although allowing a battery to self-charge is better still.

But if your system doesn't offer the necessary options to achieve that, then you're stuck.  I don't know of any USB-C docks that allow charging to be toggled.  Some USB-C docks don't provide power at all, so I suppose you could buy one of those and then keep using your manual AC adapter process, but otherwise when your system is plugged into a WD15, your battery will either charge or remain topped up.  But again, although that's not ideal, it's still better than putting a bunch of avoidable extra cycles on it.

I know it should be there, very strange that it isn't (I made sure I have the same BIOS version as well). Even weirder than that: I used to have that option in the BIOS (and I tried it, it worked just fine). A couple of months ago I formatted the system, installed a fresh Windows 10 and replaced the battery. Now I look for the option again and it isn't there. Could one of these actions have caused it to disappear?

Just to clarify, the "silly sentence" was mine, not yours :)

And I agree with you, hadn't thought of it that way.

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@sivanbh wrote:
I know it should be there, very strange that it isn't (I made sure I have the same BIOS version as well). Even weirder than that: I used to have that option in the BIOS (and I tried it, it worked just fine). A couple of months ago I formatted the system, installed a fresh Windows 10 and replaced the battery. Now I look for the option again and it isn't there. Could one of these actions have caused it to disappear? Just to clarify, the "silly sentence" was mine, not yours :) And I agree with you, hadn't thought of it that way.

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You replaced the battery?  Are you sure the new battery is a genuine Dell OEM battery?  If not, the firmware might not recognize it, which could explain why some of the more advanced battery management features aren't available.

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@sivanbh wrote:
They told me it is an original DELL battery before replacing it. I can open up the laptop and make sure. Is there something I can look for, other than "DELL" being written on it?

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I'm not sure, but even if there was something like that, I don't think Dell adds any markings on their batteries that would be difficult for a less than reputable third-party vendor to copy.  I don't think Dell has any sophisticated anti-counterfeit measures on its batteries.  And to be clear, I'm not even 100% sure that's the issue.  It just seems like a likely guess, since I don't think that anyone who got any battery replacement on this system would have to sacrifice these settings as a result.  But you could always try simply disconnecting and reconnecting the battery; you may get lucky and have those settings reappear.