Gary Coffman wrote:

diminishes as battery terminal voltage falls. Both problems can be solved
by using an LED controller IC instead of the brute force current limiting
resistors.

An example would be the LTC3205 charge pump LED controller chip. This
...
Other choices would be the Maxim MAX1553 or MAX1554. The latter can

I'd like to check those out. If you have a URL handy, it would be
appreciated otherwise, I'll search.

Another one Don Foreman found is
http://www.supertex.com/ and look at the HV9903.

Ted