RE: How long does a battery receiver charge last?
That's pretty much what I do.
With that setup you will be generating 2.1 to 2.5 watts or even slightly more, so I would recommend upping the wattage rating on the resistor. The setup will draw anywhere between 436mA to 533mA depending on the particular resistor (5% tolerance - gold band) in case anybody is wondering.
If you use conservative quitting voltages you will be fine.