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4 AA extra power pack for smartphones & other USB devices?

Hi,

I recently came across a "Rayovac Rescuer" in Target or somewhere similar. It has a USB power output which you can use to top up a smartphone or similar device "in the field", & takes 4 AA cells --- either alkaline or rechargeable, but you can put rechargeables in it & use a USB cable to charge them up (I'm not sure if you use the same USB port for charging the batteries up as for discharging them into your phone). Can this thing be any good?

ISTR that you need a slightly higher voltage to charge cells up than they provide, so can a 5 V DC input charge a set of rechargeables up adequately so they can put 5 V DC out later?

Thanks.

--
There are some things that are not sayable.  That's why 
we have art.                     --- Leonora Carrington
Reply to
Adam Funk
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phones run on lithium polymer cells ( 3.6-4.2V ) and will charge from anthing above about 4.5V

USB power is 4.75 to 5.25V DC

A series battery of 4 rechargable AA cells is about 4.4V when depeleted and 5V when full, mostly about 4.8V

so you couild charge and discharge through the same connector, but it's better to remove the cells and use a dedicated NiMH charger.

--
umop apisdn
Reply to
Jasen Betts

Thanks for clarifying that. From googling around, it seems that the

(alkaline). I might try one of these things if I see it again.

--
If hard data were the filtering criterion you could fit the entire 
contents of the Internet on a floppy disk.         --- Cecil Adams
Reply to
Adam Funk

So what would happen if I just wired 4 AAs in series between the ground & power wires of a chopped USB cable & tried to recharge a phone with it? How about a resistor in series to limit the current?

(I'm wondering how much "stuff" there is in the Rayovac Rescuer other than the battery case.)

--
"It is the role of librarians to keep government running in difficult 
times," replied Dramoren.  "Librarians are the last line of defence 
against chaos."                                       (McMullen 2001)
Reply to
Adam Funk

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