Comparing Amp-hour ratings between PbA and LiFePO4 is tough. Peukert’s exponent explains the capacity expected from a PbA cell at given discharge currents. The equation is:

I^x * t = Ah

I = current discharged

x = exponent

t = time

Ah = total Ah's

Most PbA cells have a Peukert’s exponent rating between 1.3 and 1.6. Good PbA cells have an exponent the gets closer to 1.15. We can’t assign this exponent to LiFePO4 because of chemistry differences, but an approximation of the Peukert’s exponent for comparison would be 1.05 for LiFePO4. As an example, a 20Ah LiFePO4 cell will produce approximately as much or more power as a 50Ah PbA cell at the same rated voltage.