> He only intends to run the PIC off the 5V, the LED's go straight
> off the battery (at whatever V that may be)

TBH, and this is not a good day for paying attention to what other
people are doing, I've lost track of exactly where this project is at

What I'd start with -

4 x AA (or even C cells) and a 5V LDO for the PIC
A DC jack so that any convenient power-pack can be used
High-efficiency individual LEDs run off Vbatt
PWM driving
Vbatt and ambient light monitoring to auto-adjust PWM

Re-design cross-point switching arrangement to reduce PIC size
and eliminate either high-side or low-side drivers

Maybe using low drop-out switches, such as the DG411 (30mA
per input, suitably power-rated, but circuit can be arranged so that
switches within each IC do not control combinations of LEDs that
would exceed IC wattage rating)

Maybe shift registers to low-side control any combination of LEDs

Maybe something like Maxim's port expanders as a matrix driver

Maybe I shoulda been in bed an hour ago. Maybe I am. Maybe this
is all a dream. Had better

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