Battery pack question

Ok this might be a stupid question!

I have a battery backup pack for my iPhone that has excellent storage and high mAh. It has twin outlets to let you charge two things at the same time. The outlets are 5v as per usual for USB. I can get USB to 2.1mm power plug cable. As rechargeables are usually lower voltage than standard batteries is there any way I can link the two cables to provide 10v? This way I could run a boombox through the 12v input socket.

Or would it blow up lol

Ummmmm, I think we're going to need Norm to explain in detail why this will not work, but I am certain it will not!

Well I kinda thought it wouldn't because it would be too easy lol

Might just try it and see

I am no Norm but the current draw would be to much not a good idea to link them .

It risky to run on lower voltage. A bit higher is ok. You could run them in series but would suggest using 3 making the line voltage 15v dc. The output of one battery pack would be parallel so you need three separate battery packs.

Sorry to tell you, but those charging power supplies are not working like batteries. In other words, if you connect +5V and +5V wires there are two things that could happen: nothing or you could produce some smoke from electronics (boombox and/or charger).
The thing is, the power supplies in such chargers are usually switching type, meaning that they chop and transform MAINS voltage through tiny transformer, and tend to monitor the outgoing voltage.

If you really want to supply the box using PSU, maybe you could get this one: http://pcengines.ch/ac12vuk.htm from http://pcengines.ch/newshop.php?c=2

Yes, I know they/you are supposed to use them with their Alix boards/computers. I have used EU versions for years and they are rock solid, very durable. Best buy in my book.
@hopey: I am not shure I understand you. How do you mean running on lower voltage is bad? Is it not just the case when the batteries are a bit empty? They do give lower voltage when they are emptied. Also, the NiMH rechergable batteries have lower voltage to start with. On the other hand, I agree 10% more or less of the nominal voltage should be OK. YMMV.

If you run on lower volts the capitors will attempt to charge up to line voltage and will over heat and fail.

Hm, I was under impression that we were not talking about line (mains) voltage, but about low voltage - on secondary side of PSU.