You will run from 99% of wild battles. Wild Pokemon give no EXP, so fighting them only risks status effects and wasted PP. You are only battling to level yourself —to learn the AI, to test damage rolls, or to catch the Pokemon.
If you want to try this yourself, you don't necessarily need a pre-patched ROM. Most players use the Universal Pokemon Randomizer (ZX) Load your legal ROM. Navigate to the "Misc Tweaks" or "Standard Tweaks" section. Check the box for "Give No Experience." Final Verdict pokemon no exp rom