Well, I want some of those 7Ah batteries because they perform far far better than anything else on the market. Im with Daniel and Ed on this one, its just not possible for a 7Ah SLA to provide 250A for one minute. A really good SLA like a 16Ah Odyssey has a 4C Ah factor of about 40%, this further reduces with higher drains. If we were really generous with your 35C drain and assumed 25% Ah efficiency then your 7Ah battery would only last 25 seconds at 250A. The power dissipated in your battery assuming a typical internal impedance of 28m Ohms would be 1.75kW i.e. meltdown. As Ed suggested, the maths is getting boring.

Paul