How should I connect multiple Lithium Polymer battery packs in parallel?
Alternatively, you could use one larger battery with one regulator.  It saves power, is even easier to charge, is still regulated, and you can scale the battery to your power requirements.

You could use a boost converter with a 4.5V source, or you could use a 6V battery with a buck converter, or you could use a linear regulator such as the LM7805 for a noise free source with more power loss.  If you need more than the rated 1A, there are bigger, better regulators out there for sale.

Connecting regulated outputs is always asking for trouble in my experience.