The main differences are:
1) Battery: AC300 has no built-in battery and must work with B300, while EP500Pro connects with B300 only for capacity expansion.
2) 30A AC Output: EP500Pro has an L14-30 port while AC300 has a TT-30 port.
3) Maximum Input: 5,400W for AC300 with two B300, 3,000W with one B300, while 4,000W for EP500Pro.
4) Weight and Dimensions: AC300 is smaller.