What might cause this USB cable problem?

Factual Questions
1

Whenever I buy a new USB cable for my phone, for a few days or weeks it may charge at a good speed, but then gets slower and slower. (Currently it is a USB-C cable but I had tge same issues with earlier plugs.) My latest phone came with a USB cable that I managed to use for well over a year (probably a record, by far) before it died, and it worked well. But now I’m back to the bad old days. The batch of 3 cables I bought 2 or 3 months ago started off charging adequately if it at peak theoretical speed, but now all 3 have degraded to the point that I at best break even while using the phone as it charges (meaning that it stays at, for example, 80% the full time I’m using it) but more likely have constant discharge: the charge goes down during use but more slowly than if the phone were unplugged. The charge only goes up if I’m not using the phone (screen off, left alone) and then takes hours to go from 80% to 100%.

Using Ampere I see occasionally that the phone is charging at around 200 mA, fluctuating a bit in either direction. But it does sometimes show a rate higher than that (lately up around 600 mA) briefly, indicating that the cable can support that but the phone’s charging circuitry isn’t accepting it.

This is a pattern that has happened for years across multiple phones, multiple chargers, and an obscene number of cables. Any ideas why it happens? From past experience if I buy a new cable I’ll have a decent experience for a few weeks at .ost before I start having constant problems again.

(And now I’m at 68 percent and will set the phone aside for a few hours in the hooes of getting back to 100.)

2

I’ll go out on a limb and say the cables are not causing your troubles. You’ve tried many; they all do the same thing; and the phone is the only constant in all configurations.

What type of phone, how old is it, and what operating system (and version) is it running?

Some mix of a dodgy battery and an overzealous (or appropriately zealous) power management system on the phone could lead to poor or inconsistent charging. The phone/OS can slow down charging if certain battery life settings are enabled or if it senses a problem. It could even be an over-temperature or temperature sensor issue, for example.

Edited to add: I see you say this is over multiple phones. In that case, I’ve got nuthin’. (I would say that you’re seeing the transient improvements because you do something when it gets bad, like use/charge the phone less until you get a new cable (altering the typical charge state) or simply buying a new phone because of the degraded charging. But that’s pushing against the premise, and I imagine that would be an annoying and unhelpful first answer. :slight_smile: )

3

There may be multiple things going on here.

First the cable one. Bending and flexing cables will cause the connections and wires to degrade over time. The faster and higher voltage charging speeds require certain cable qualities to work. For example, when shopping for USB-C cables, you’ll see some will say they support 100W, but others will not. A 100W cable will be necessary to run a laptop, and should do a fine job charging your phone. Until the connections between the wires and the connectors wear out, and it stops working well.

For some reason, Apple lightning cables are the most likely (in my experience) to become useless after 1-2 years.

The second thing is that almost all smart devices now regulate how they charge to preserve the service life of the battery. Many phones will charge to 80%, and then pause. If your phone is stuck on 80%, it might be something the phone is doing in on purpose to prevent overheating and to preserve the life of the battery. For example, when I plug my phone in at night it will charge to about 80%, and then slowly charge to 100% so that it reaches full a bit before my alarm goes off.

Along with limiting the maximum charge, the rate of charge will also change based on the how full the battery is. When nearly empty, the battery will charge at a high rate. As it gets more full the charge speed will slow down. I see this in things as disparate in battery capacity as my watch and my car. My watch noticeably slows it’s charging speed at 80% capacity. It might take 50 minutes to go from 10-80%, and another 20 minutes to get to 100%

4

What kind of phone, which specific cables, and what kind of charger? All three are important.

Generally speaking:

  • You need a charger capable of outputting USB-PD at a wattage that your phone wants. Not every charger can. The low-quality ones will be intermittent or not work at all.
  • Your cable also needs to support that wattage.
  • Your phone model matters too, as does its temperature (i.e., make sure it’s not overheating).

Without any specifics, if you have a relatively recent name-brand phone, you should be able to get a good Anker charger and cable like Anker Nano Charger (45W) with USB-C to USB-C Cable - Anker US and be set. There are even higher quality cables, like Anker 643 USB-C to USB-C Cable (Flow, Silicone) - Anker US

If you’re buying random no-name chargers or cables, it’s hard to verify their quality. USB-PD is incredibly finicky and requires two-way communicates from the charger through your cable to your device to confirm the higher power. A slight kink or loose connection could break part of that communication and lower the charging speed back to the minimum. The cable goes from “smart, USB-PD properly supported” to “dumb cable delivering minimal power” with the slightest damage.

The amperage won’t change much and your phone can’t always detect how fast it’s charging (or rather, most phones won’t allow apps to detect that information). If you really want to measure each component, you need an external hardware USB tester to check the voltage: Eversame 2 in 1 Type C USB Tester Color Screen LCD Digital Multimeter, USB C Voltage Current Voltmeter Amp Volt Ammeter Detector USB Cable Charger Indicator DC3.6-30V/0-5.1A - Amazon.com

But TLDR the spec sucks and there’s more poor quality chargers & cables out there than good ones.

5

No, as I mentioned in the OP, this happens with all of my phones over a number of years, including Samsung, Motorola, and LG.

6

As echoreply said, this part is normal. Li-ion batteries are chemically fiddly, and fast-charging all the way will degrade them. So some phones (and cars, for that matter) will only fast-charge up to 80% and then slow-charge from 80%-100%. That alone isn’t indicative of anything wrong, if it’s consistent and not too slow (i.e. it still charges to 100% overnight).

On some phones you can override this if you really need to fast-charge that last 20%. Check the notifications dropdown.

7

Did you use the same charger with all of them? Or the same power outlet?

8

The number 80% was chosen entirely arbitrary. The behavior is entirely the same no matter what the percentage. And yes, I’ve swapped chargers and swapped outlets. The two chargers I use right now were bundled with an earlier Samsung phone (current one is a Motorola) and with an Android tablet.

I use the app Ampere (and have for multiple years over multiple phones) and it is showing a higher charging rate right now than usual lately. It has been going down as low as 50 mA. (But my charge amount still dropped from 74% to 73% while typing this.)

A snapshot of charging

And unplugged

(And charge has now dropped to 71% while charging as I continue to type this.)

9

Again, which specific charger and cable?

If Ampere is showing the right data (I’m not sure if it is), you are charging at speeds a decade+ old, and not fast charging at all… 0.5 A at 3.9V is barely 2W. That’s nothing. Fast charging is more like 15-30W, and USB-C should up the voltage way past the old USB’s 5V. Ampere may not be able to see that part.

Are you using a USB-PD charger and C-to-C cable, or a USB-A one with a USB A-to-C cable?

It’s not their brand that matters, it’s their electronics inside. Some tablets use less than some phones. Older chargers especially are unlikely to be able to fast-charge modern devices. You can check their max output wattage on their stickers. But they must support USB-PD for proper fast charging, unless the brand happens to have its own fast charging protocol (was common a decade ago, less common now). If it has a USB-A port, it won’t work right.

Unless you are sure you have a high-quality USB-PD charger that can output sufficient wattage, along with a C-to-C cable, I am fairly certain that’s your problem.

Get that Anker Nano combo for $35 and I bet it will solve your problem.

10

Ampere also probably isn’t showing you the full picture. If it’s showing a net gain/loss on the battery, that’s not the same as what the phone is actually getting, only what’s left over for the battery.

You can get a USB tester dongle if you really want to see what the electronics are doing, or just get a new/better charger and actually make it work…

11

Have you tested that exact one? I need one that can handle USB-C. I have one that works well for USB-A, including the various old proprietary fast-charge protocols, but the one I got for USB-C is junk. It always shows 500mA of charging, even if nothing is happening. That means the cumulative charge counter is worthless, and it is basically too unreliable to inform me if a cable and charger are working as expected.

@Darren_Garrison getting an external meter is really the only way to see what is actually happening. I have my reliable USB-A one, and also a charging brick that has a builtin meter that seems reliable, and it is very educational. Chargers lie about their capabilities, cables go bad (or where never good), and devices ramp up and down their power draw.

Even an external kill-o-watt type meter can be useful. It might not tell you the exact nature of the USB signal, but if a charger is only drawing 2 watts, you know your phone is not charging fast.

12

The charger is a Motorola with nothing more than a big M in a circle on it. The three cables are called SMALLElectric. Every charger I’ve ever had came bundled with a device, no buying premium. None of them have ever supported beyond basic charging speeds. I’ve never bought major name-brand cables. My current ones were 5 for $9 on Amazon. But they worked, for several weeks, before they slowed down. (I’m now down to 66%, with “charging” happening, from the 74% earlier in this thread.) But the specific charger, phone, and cable at the moment aren’t super critical because the same degradation happens with every phone, every charger, and every cable I have used over the course of years.

13

They probably just can’t keep up with the power needs of your phone under varying load conditions. If it provides, say, 3W max power and sometimes your phone uses 2W and sometimes 5W, then it won’t always be able to keep up.

The cables probably aren’t physically degrading in any significant way, the phones are just drawing a variable amount of power and sometimes the charger can keep up and sometimes not.

What exactly are you trying to solve? If this is a theoretical academic question, an external power meter is what you need to determine for sure what is going on. If this is a practical need to keep your phone charged, get a better charger.

No, sorry, it was just a random find.

14

I had a similar issue with my Samsung S25. I found that it was charging slowly, even on the fast charger.

“Ah, bad cable” I thought. I swapped out the cable- the problem persisted

“Ah, bad charger” I thought. I replaced my old fast charger with another one- the problem persisted.

I then tried both the charger and cable with other electronics (just about every modern small electronic gadget that runs on lithium batteries has a USB-C charging port)- charging time was fine for the other electronics

I then bought an inductive fast charging pad (~$40) and tried charging my phone on that- charging worked fine and fast!

So, reluctantly*, I admitted that I had somehow damaged the port or its connections and took the phone to a shop to fix it, which they did in an afternoon.

The inductive charger? That’s now my overnight charging station, but in the car and on travel, I use USB-C fast chargers plugged into the phone.

*I’m someone who was “raised in the lab” with cables very much more expensive than USB cables and formed a habit that I would advise everyone to cultivate. 1) when plugging a cable in, always hold the plug exactly aligned with the receptacle. When disconnecting, grab the connector (not the cable) and pull out exactly aligned with the receptacle. Saves wear and tear on both cables and connectors.

15

Another thing that can slow down charging, mostly unrelated to all of the other things mentioned, is pocket lint getting in the charging port. The lint keeps the cable from seating correctly and making a good connection. Usually this causes intermittent charging, not slow charging.

USB-C ports have a delicate blade inside, so I don’t know what the best way to clean them is. Perhaps a sewing pin or compressed air? The Apple Store will clean out ports on Apple devices for free.

16

I’m trying to get my phone to actually gain charge while it is plugged in and in active use instead of losing charge. In other words I’m trying to get the phone to act like it did 3 or 4 days ago with the exact same charger and cables. (I have been letting it sit idle since time of my last post and the charge has gone for 68% to 93%. But it has dropped down to 92% while I was typing.)

17

If 500 mA is the fastest it ever goes, then that charger is probably not providing enough power for the phone. You can see that sometimes, when it’s not plugged in, it’s using -630 mA (maybe even more under heavy load, or when it’s downloading stuff or using the cellular modem or GPS, etc.).

You might be charging it successfully when it’s not doing anything, but the moment you pick it up and start using it, it could be using more power than the charger can provide.

My question is… do you have to limit yourself to such a slim margin of error? If you get any half-decent USB-C charger, you would easily get 20-30W+ and not have to worry about this anymore. If cost is an issue, even a cheaper 10W or 15W would still be a huge improvement over what you have right now.

There’s a thousand ways we could guess at troubleshooting, but at the end of the day, even at its fastest, it is not putting out enough power.

For reference, the charger that normally comes with your phone is 10W (Specifications- moto g stylus 5G (2022)| Motorola Support US), so that is what the manufacturer expects it to get.

With Ampere it’s hard to tell what’s going to the battery and what’s just being used by the phone (i.e. you don’t know the actual power you’re getting from the charger, only what’s going to the battery), but if it’s really anywhere close to 2W, that is 5x LESS than what the manufacturer normally provides with the phone.

Perhaps there is some minor mystery here in terms of “why it was working a few days ago”, but chances are even then it wasn’t really, except when the phone was entirely idle. Even if you managed to figure out the specific reason (cable degradation, lint, broken port), you still weren’t giving it enough power if 500 mA at 3.9V was all it ever got. If this is the same situation you’ve experienced with multiple chargers, but all of them were recycled/hand-me-down chargers from random other devices, it’s likely that none of them were making enough power to begin with.

Do you not have the original Motorola charger that came with your phone? That should provide enough power. 10W is a huge difference.

I hope this doesn’t sound argumentative… it just seems the most likely cause given everything you’ve described so far.

18

But it isn’t. This has gone as high as 1,800, even with these specific cables I have now when they were new. But then after a few days a cable will rarely pass 1000. Then in a few weeks it will rarely pass 600. In a few months it is lucky to break 300. When I eventually buy a new cable the pattern starts again. I’ve been sayin that this whole thread: it starts off with adequate speed then degrades. And this kind of thing has happened for years, with Mini USB, Micro USB, and USB phones and chargers.

19

I know that you are trying to be helpful, but you really don’t understand my situation. My standard operating situation is that my phone is only actually unplugged for a couple of hours a day. Any time I’m staying in place near an outlet, the phone is plugged into the charger. While plugged in and being actively used the phone stays at 100% charge. It is only below 100% charge for maybe 3 hours a day (usually no lower than about 60%). With very heavy use. So this experience of losing charge while plugged in is absolutely, positively not the way it normally is. (And now that I look, I am using the charger than came with the phone. I thought it was from an earlier Motorola phone, but I notice now that it has a “10” molded into the plastic.)

20

Here I meant “and USB C”.