I didn't see any dedicated post to this, it looks like some who upgraded the LCD screen also switch to two rechargable lithium ion batteries, then used a step up converter to raise the voltage.
I have been thinking about putting in 3 or 4 then using a step down converter. How many people have down this, initially there appears to be room for it. Looking at the lynx schematic though it looks the lynx it's runs off 5v.
I think I have seen posts where the remove a zenor diode or convert it to run at 5v volts but I wasn't able to flush anything solid out of the forum search. I seem to recall reading though the mod results in parasitic battery drain. Hopefully someone can clarify this for me as well.
My lynx died a little while back, so I have purchased a cap kit, replacement mosfet and LCD upgrade. That had me thinking this would be the opportune time for upgrading the battery as well.