Hmm, LeafGreen uses CR1016? Good to know. I've only seen CR2025 in GB/GBC cartridges, and actually never opened GBA cartridges.
I havent had any battery issues other than my PK Silver one, but like it was said earlier, that generation had their battery issues because of the internal clock quartz crystal that needs power.
What puzzles me more is that I've yet to figure out how the NeoGeo pocket keeps its saves. Took one cartridge open one day and discovered that it didnt have any battery, the internals were rather simple actually. So I assume it has a non-volatile memory of somesort.