Battery Extender for C500/SMT-5600?

[Guest sracer]

Hi all. I've only had my vox SMT-5600 for about 5 days and I'm already pretty well hooked up... BT folding keyboard, 512MB mini-SD, odds-n-ends software. The only thing missing from my "road warrior" arsenal is a battery extender.

When i owned PPCs, I purchased external battery extenders for extended use on flights. (a little box containing 4 AA batts that attached to the sync/charge port of the device).

So I'm looking for such an accessory for the C500/SMT-5600. I've searched around but only found a universal battery extender with a USB attachment. I don't know if that would work... and rather than take any chances, I'd like to know for sure.

I guess worst-case scenario is that I purchase a few replacement batteries, charge them up and have them as spares. (I much prefer to have the flexibility of using AA batteries though).

Thanks in advance.