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

Question

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.

Jasen Betts · Accepted Answer

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.

Adam Funk · Answer

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

Adam Funk · Answer

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)

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

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