Reverse USB Chargeable Component

The 5 volt line on the USB connector is the output of a voltage regulator and not a direct connection to the battery, so you can't charge the battery that way.

Once I turn my laptop off none of the USB ports is powered.

(The 5 volt line on the USB connector is the output of a voltage regulator and not a direct connection to the battery, so you can't charge the battery that way.) I do understand this, I guess it was wishful thinking that with all the new technology out there maybe, just maybe someone had seen something that might do what I am looking for. I do understand that once one turns off the system that the usb is off too and, that there are power packs out there. Thank you all for your feedback Gary

What you may have in mind is to be able to use the USB 5-volt output level to charge other accessories?

1. This may only be possible if the accessory is also powered by a 5-volt battery and only require a small amount of current to operate..

2. Otherwise the USB 5 volt level has to be converted to a much higher voltage like 15 volts to charge a 12-volt powered accessory...

3. Although #2 above is very doable, charging a higher voltage operating accessory will still be a problem.. not possible!

To effectively charge any battery, we need both the voltage and an abundant supply of current! And since the USB available current is very limited, it is not capable to supply your needed current.... it is not going to work!

Most cell phones use 3.7 or 4.2 volt battery thereby, less than the 5 volt usb level. However, when I connect the cell phone to the usb charging connector of the device via female/female usb, it did not effect my cell phone i.e. Usually when I hook up my cell phone to charge it the battery gauge lights up. In your 1. (This may only be possible if the accessory is also powered by a 5-volt battery and only require a small amount of current to operate..) I read as a possibility especially being the cell is less than 5 volts or am I misreading it?

You read it correctly. The problem that I can stipulate that is causing the inability to charge your cellphone are;

1. The USB available current is very limited.

2. Your cellphone is powered or turned On when you tried to charge its battery?

3. Which means the available power from the USB port being limited is not enough to effect any charging...

4. So you need to turn off the cellphone, and be sure no other USB ports are being utilized by other accessories!

5. At this point the USB power may be enough that it may start to charge your cellphone battery very slowly!

6. Consider that #5 above is not guaranteed... If the cellphone battery condition is fully depleted, it will completely pull down the current limited USB power and therefore no effective charging takes place!

Good luck!

If it's emergency USB power you need, there are USB battery packs on the market.

You can't share battery charge between cell phones, because they have a diode in the input to protect from reverse polarity and avoid discharging thru a charger that is OFF, so a cell phone takes but doesn't give.

There is not any advanced technology capable of reversing the current flow across a diode without burning it.

I have a small emergency cell phone charge pack that uses 2 lithium penlights to provide power at 5 volts with multiple cell phone adapters (purchased about 8 years ago) that has a small boost converter to up the voltage. I have used it with different cell phones over the years, Motorola, LG, Apple, also USB Not sure who made it, seems to be good for 2 hours on high current devices, 6-8 hours at lower currents. Complaint: lithium cells are expensive, alkaline doesn't last as long.

The logical problem would be that none of the devices would know which one you want to charge.

Phones can be charged from Laptops that have a "hot" USB which allows charging items even when the laptop is off. They are usually marked red with a flash. Laptop needs to be on charger for this.