They don’t for anyone else.

Tell us exactly how you measured the decline in power.

Edited to add: A google search turned up no relevant results.

Bob

Interesting. I've seen it across almost all USB ports on all devices. Forget PC USB ports.
One of the first things I notice is that charging becomes slow to sluggish.
Even with a new battery. I sometimes use something like this.
You plug it into a USB power source, then plug a USB device into it and it measures the voltage and current based on the load.

If this is a very rare occurrence, then obviously I am doing something different to cause this and I need to re assess.

 

Using the USB port of a peronal computer for battery charging is at best a very poor choice, unless the PC is otherwise worthless. Buy a $5 charger and use it instead. PC usb ports are intended to power a mouse or a similar load, they were not intended to charge every item around. It may also be that the ports you are using have become worn or dirty. Both will add series resistance.

In addition, the charging current into a battery is forced only by the difference in voltages between the battery and the charging source. so as the battery voltage rises the charging current will drop. And so if the voltage drops just a bit it will just barely charge.

Agreed, and I rarely do. About the only device I will charge with a PC is my bluetooth headset which draws only a tiny current.
That said, every time you plug your device (cellphone or camera for example) to transfer photos or data, you are charging the device from the PC while it is connected under many circumstances. A lighted keyboard can draw almost as much current as a small cellphone.

Perhaps the ports are becoming "dirty". But that would be odd that I'm the only one who gets dirty USB ports.
I'm fairly picky about electronics and I thought I took better care of my electronic devices than average being careful with them and keeping the dry, clean and away from moisture, foods etc.

 

batteries is one thing I'm probably well above average in knowledge.
I've done extensive reading on most types of batteries from 18650's to LA, SLA AGM, LiIo, LiFePO4.
I'm familiar with their chemistries and differences.
I know most of the discharge and charge rates and curves and recommendations for them all.
I know all about float charge, saturation charging, absorption and bulk charging.
I know all about internal resistance, how to test it (the long way) and have equipment for doing so as well.
I build my own battery packs from 18650, LiFePO4 cells and many others. And have a lot of equipment for testing them.
I was into RC models for 40 years so knowledge of batteries runs deep.

I own a number of Riden power supplies among others and have a number of capacity testing devices.
Just to clear up any confusion about my confusion with batteries

What I am not keen on is USB ports and why they decline in power output.
However, the suggestion in a previous post about how resistors increase in resistance and IC controller chips can become bad are very useful.

As always, the assistance I get here is always very appreciated and respected.

Well, forgive my suspicions of someone who might not have known or had as much experience as you apparently have. Thing is - some people come here with a preconceived notion of how something works, and sometimes those notions are in error. Well, looks like I'm the one in error this time. So I'll sit quietly and follow this thread for a bit. But unless I have something solid to add - I'll remain quiet. But thank you for clarifying your knowledge base.

 

Those voltages are all within the normal range and well above the terminal voltage of any common battery that is charging. The problem therefore is much more likely to be due to the battery rather than the charger. As DP mentioned, batteries lose capacity as they age.

Lose Capacity and also often the battery's internal resistance increases with time/charge cycles/overcharging

 

Very good information. Thank you.

Whenever I connect a device to USB that draws a current, let's just say a cell phone for example, I have no control over the current draw. it seems that whatever device with a battery that is connected will draw as much current as it can and often that exceeds 500mA.;....or used to.

A resistor that has increased in resistance will limit current but leave voltage alone right?
This sounds precisely like what is happening.

A resistor which has increased in resistance needs to be replaced under every circumstance IMHO

 

Lose Capacity and also often the battery's internal resistance increases with time/charge cycles/overcharging

Yes. So I made sure the batteries in question met OEM specifications for IR