5V External Supply

My circuit does not have a built-in power supply, it's normally fed direct from computer USB or a wall-wart, but now I want to be able to run it from an external battery. I need something like 60-100ma

I bought a USB portable power bank http://www.amazon.com/Tenergy-2600mAh-Lipstick-Portable-Power/dp/B0097CWOO2/ but I find that it drops its output briefly to 3.5V every 10 or 11 seconds. Needless to say, that's not ok!

This sounds like the problem described by Paul on dorkbotPDX http://dorkbotpdx.org/blog/paul/battery_pack_load if the circuit doesn't draw enough power. He solves it with a circuit that keeps the USB supply alive with a dummy load that kicks in briefly every 1.4 seconds. I would prefer to avoid the clutter if I could.

I could try another brand or I could roll my own with a 9V battery and a 7805. I wondered if the mintyboost type of supply would have the same problem.

Get a 5V booster and run it off 2 or 3 AA batteries: http://www.ebay.com/sch/i.html?_nkw=5v+dc+boost+pfm

If your power bank is new, you can disassemble it in order to use its battery(ies). You can get 5v boosters with also charging circuit.