Battery overcharing

[PlainName]

We all know by now that charging a Li-xxx battery to full every time, and especially keeping it on charge, is not good for it. My new phone says not to leave it on charge, and especially it could have Bad Things happen if it's on charge for 12 hours or more. That's kind of problematic why the best time to charge the thing is overnight and you're not going to be awake to unplug it when it's full.

So why don't they just turn off the charging circuit on a full battery? They know when it is full, or nearly full, and surely it's simple enough to just flip off a MOSFET or something in that circumstance. But, no, it takes a fully working external human being to achieve that.

What have I missed? I looked for USB cables, or chargers, that could detect a reduced current and just turn off at that point, but there are very few. Amazingly few, actually. With USB PD didn't anyone think to enable the phone to say "Full now, thank, check back in a bit"?

Also kind of surprised there is no phone app that can monitor charge state and, when it thinks it's gone on enough, trigger an IoT socket to turn off the charger.

Seems to me either overcharging isn't actually a problem or fixing it is so complicated no-one tries.

[Andy Chee]

My old iPhone 7 (released in 2016 and still going strong) definitely has charge management i.e. it can disconnect the charger.  So I'm surprised your new phone lacks that capability.

[PlainName]

Me too! But it seems to be common and not just this phone - I mention this one simply because it's the thing that bugs me at the moment

[elektryk]

On rooted Android device you can set charging limit for eg. 80% with app. Also my old Latitude notebook has such option in manufacturer's software to extend battery lifetime while it is mainly used on AC.

[themadhippy]

What have I missed?

The profit from selling you a new battery/phone because the old one no longer holds a charge

[Siwastaja]

What have I missed?

Probably two three things:
1) Leaving the charging circuit "connected" i.e. floating the battery is not significantly worse than disconnecting it. Sources that claim this are wrong. There is a lot of wrong information out there. Especially if you try to deduct technical details out of manuals written for ordinary people, you are prone to making wrong conclusions. Consumer manuals are usually shit. For example, many Ni-Cd/Ni-MH era instructions (like "you have to charge the phone overnight before first turning it on") stayed in manuals for over a decade after li-ion became a thing.

2) Microcycling (stop charging - voltage drops because of use - start charging again - stop charging...) the cell near full charge probably isn't any better, and is likely worse than just floating it.

3) Many charging circuits stop charging anyway, you just don't know it's happening, so your assumption of them not doing this is likely wrong.

Note that the 5V wall plug is not the charger. It's a power supply which supplies power for the charger, which is inside the phone/whatever device.


+ holding the cell at full charge voltage is not "overcharging". Overcharging is going beyond the full charge voltage. (If we are pedantic, then the equivalent holding voltage would be a tiny bit less than stopping voltage, but the difference is small, e.g. 4.15V instead of 4.20V; in such pedantic analysis, then holding at 4.20V is technically overcharging, but still within the tolerances of the battery specification, so maybe not "overcharging" after all.)

[Buriedcode]

AFAIAW all phones will manage charging, including sometimes preventing charge to "full" based on age and battery health.  Even my old cheap Huawei with generic/vanilla Android does this.  There is no need for any kind of technical solution on the part of the consumer - I'm sure there are "special charging cables" that can claim to maintain battery health, but that would be marketing wank.

Also, as noted, there is a lot of vague (and wrong) information regarding battery life, care, charging technology that is often perpetuated by those with poor understanding ("tech journalists") and cheeky marketing tricks - like claming faster charging times simply by not charging to full capacity, or making odd comparisons to old NiCd tech.

I suspect your new phone has that warning - not because there is a real need for human intervention to prevent abttery damage, more as a safety precaution since phone manufactureres really dont' know if you're going to leave your phone on charge, plugged into a really dodgy USB supply, next to a radiator.  Even then its internal sensors will stop the charging, but charging creates heat which may or may not reduce the phones life in situations where there are other sources of heat.  I think its more a safety message to cover themselves.

Note the old idea that you should let your phone run down to 0% then charge it fully when you first use it is to train the battery supervisors culomb counter for accurate battery level estimates - not for actual battery health.  I'm not sure thats really needed these days.

Edit: typo.

[BrokenYugo]

Sounds like the generic copypasta warnings you find in cheap device manuals to me, pay it no mind.

What you shouldn't charge more than 12 hours are NiCd batteries on really basic dumb chargers with no cutoff feature that just dump endless energy into the battery. Crappy cordless drills a decade plus ago.

[PlainName]

Thanks all for your comments, where y'all seem to be agreed that worries about battery wear are unfounded. However, I use an app called Accubattery which keeps track of charge and usage history to determine the battery health and likely time to running out. Of course, the first thing that springs to mind is that they have a vested interest, but they also publish the research which goes towards the app development.

For instance: Charging - research and methodology.

So I am not sure it is as clear cut as might be first thought. And, hence my question (which, thanks Siwastaja for clarifying, may be confusing!).

[SiliconWizard]

What is your new phone?
Of course any phone with a li-ion battery has a charging management IC that won't allow "overcharging", that's just not even possible. Even the 10-cent (or less) Li-ion charger IC does that.
What it looks like is some copy-pasting, not from any existing end-user device, for which it's not an issue, but from battery datasheets themselves, which makes no sense for the end user.

[PlainName]

For reference, I would think that big name manufacturers would know about the product they are shipping. Here's a sample:

Xiaomi (my emphasis)

Avoid full charges

Li-ion batteries work best when the charge span is between 20%-80%. Going from 80% to 100% actually causes it to age faster. Consider the last 20% as extra in case you are not free to put your phone into charge but do top it off by charging as long as you can. Li-ion batteries works best in the middles.

This is not to say you should never fully charge your device of course, because we do need it at times like for battery calibration or whatever reasons you may have however you should always keep in mind to avoid it. It goes without saying that charging over night is not a great idea unless you are controlling the charge flow like stopping it at a certain battery level.

Nothing Tech

6. Avoid excessive charging
If the mobile phone is fully charged, the charger will be maintained in a full power state. This may cause battery deformation and the leakage of the fluid. The performance of the battery will also be significantly reduced and damaged.
Do not exceed 12 hours continuous charging time. When the phone prompts are full, you should unplug the charger.

Samsung

Unplug the charger after the device has reached a 100% charge to avoid a swollen battery

OnePlus

You should not charge the battery for more than 12 hours. After the phone is fully charged, unplug the charger.

[PlainName]

What is your new phone?

It's a Nothing(1). Current phone is a Xiaomi A1. Been trying to find a suitable replacement for some time, but nothing (not the phone!) ticks all the boxes yet.

[Kim Christensen]

For reference, I would think that big name manufacturers would know about the product they are shipping. Here's a sample:

Interesting. I wonder how much of this is just them covering their asses in case something goes wrong and things catch on fire.
Like the OP said, it seems pretty stupid that a "smart" phone can't manage it's battery properly.

[PlainName]

My guess is that a simple battery charging chip is used, which basically allows charging at some maximum rate and reduces to a trickle, or keeping topped up, when they battery is up to some specified voltage. As such, it's 'safe' in that it's a controlled charge, but it's not controllable by the phone per se. It's hardwired.

Some devices - Apple, presumably - add the necessary stuff to allow the phone to affect the charging, perhaps the rate and certainly the termination. Obviously, that would cost more and not be as simple as just using a charge chip.

[Siwastaja]

If you want true, real lifetime increase, you:
* Keep the battery significantly less than fully charged. 95% or 90% does not cut it. Go for 60-70% and below.
* During charging, avoid the combination of high state-of-charge, high charging current and cold temperature. You can pick one pretty safely. Pick two, and lifetime decreases significantly. Pick three and it's a disaster. Products of course do manage these things automagically and prevent very bad conditions (e.g., limit charging current at cold temperature; slow down charging near full), but they are not too aggressive to limit your use. If you want to optimize the lifetime, it's good to know these relationships so that you can manage more strictly than the product firmware does.
* Avoid storage at high temperature and high state of charge.

[Siwastaja]

For reference, I would think that big name manufacturers would know about the product they are shipping.

This is almost always wrong assumption, go figure. Of course their engineers know the product very well, but the manual is almost never correct at all, they are full of totally made-up bullshit to the point of making us engineer-minded lose hope in humanity. There always are managers who think that giving correct information is "too complicated" for "regular people", and solve the problem by lying, similar to "santa claus exists and gives you presents". The result is something that benefits no one, but laws require to have manuals no one reads, so then you have lies.

Specialized laboratory equipment etc. is in much better situation because the engineers can write the manuals.

[Halcyon]

There is absolutely no issues with leaving a phone plugged in for extended periods. You won't over-charge the battery doing this. The charge controller will simply stop charging when it's complete.

[PlainName]

I just charged my phone until it said full, and then left it. It was constantly sinking 4W. Should it not have been taking 0W?

[Kim Christensen]

Should it not have been taking 0W?

No. The phone itself will be using power even though the battery is finished charging and not taking any current.

[Dacian]

A battery phone keep at 100% SOC will get damaged fairly fast.
In average on my last phone I was replacing the battery every 2 years because it was mostly plugged in as phone is used as a WiFi hotspot.
Recently I got a CAT S22 Flip and likely due to newer OS (Android 11 Go) there is now an option for the battery to be kept in the 50 to 70% SOC range while plugged in and this should improve drastically the battery life. So hopefully I will need to battery replacement for this phone at least for the next 5 years.

The other phone I have is BLU with older Android 9 and that is missing this future and on top of that it keeps the battery at 4.3V so not sure how much it will last (I think is about 6 months since I started to use it in same way always plugged in) so far it seems fine.
I will be able to see the battery bulge as all my phones have removable batteries. The old one was also  BLU I think android 4 and after the third battery died I decided to upgrade.

[PlainName]

Should it not have been taking 0W?

No. The phone itself will be using power even though the battery is finished charging and not taking any current.

Yes, I realise the phone will be taking power, but it is asleep and if that state takes 4Wh then the battery would last less than a day with the phone doing nothing.

[Kim Christensen]

Yes, I realise the phone will be taking power, but it is asleep and if that state takes 4Wh then the battery would last less than a day with the phone doing nothing.

It may not go fully to sleep while it is plugged in.

[nctnico]

There is absolutely no issues with leaving a phone plugged in for extended periods. You won't over-charge the battery doing this. The charge controller will simply stop charging when it's complete.

But still, it is better for battery life if the battery is not charged to 100% but to a significantly lower level. Also, many phone chargers, charge at the maximum current. Some phones even claim to fast charge to 100% in 10 minutes or so. This is something you don't need when your phone is charging overnight.

[Halcyon]

There is absolutely no issues with leaving a phone plugged in for extended periods. You won't over-charge the battery doing this. The charge controller will simply stop charging when it's complete.

But still, it is better for battery life if the battery is not charged to 100% but to a significantly lower level. Also, many phone chargers, charge at the maximum current. Some phones even claim to fast charge to 100% in 10 minutes or so. This is something you don't need when your phone is charging overnight.

Yes, absolutely. But I bet you 99% of people out there don't bother with things like SoC (or even know what it means in any kind of meaningful way). Hardware and software manufacturer's know this.

Phones have been designed to be charged to 100% for decades and left plugged in common scenarios (in a car, while sleeping, on the kitchen bench, in an office until it's ready to be used etc...). Modern phones and laptops also tend to adjust their charging based on your habits. For example, I mostly keep my phone docked when I'm working from home, so my Google phone knows to just charge it using low current. Likewise, my Macbook will only charge to 80% as I mostly use it docked as well.

I'm the kind of person who generally keeps their phone for 3-4 years before replacement, and I've never had a battery prematurely fail or suffer significant degradation.

What we're discussing here has already been thought of and solved (at least by the reputable manufacturers). Your mileage may vary if you're buying Huawei, Nokia, OPPO, Xiaomi, ZTE, or those in the budget categories.

[Siwastaja]

I just charged my phone until it said full, and then left it. It was constantly sinking 4W. Should it not have been taking 0W?

It should not take 0W, but whatever the phone itself is using. 4W sounds very high unless you are playing games with it, though; for a typical let's say 16Wh battery capacity you would fully drain the battery in 4 hours! 4W should feel like significant amount of heat. I see two possibilities:

1) You simply measured wrong. How did you measure?
2) The battery was not fully charged yet and that power was flowing into the battery.