way to calculate the draw limit on a battery
The 'draw limit' on a battery would depend on the required discharge time.
The ‘C’ rating of a battery indicates its capacity in ampere-hours (Ah).
‘C’ would be followed by a number (C10, C20 etc.) which indicates the number of hours the capacity would be distributed over.
For example, a battery having a C20 rating of 100 Ah would deliver a constant current of 100/20 = 5A for 20 hours, with its terminal voltage not going below the specified lower limit (end voltage).
This information would be available in battery data sheets, extending down to C0.5, C0.25 etc.
The following example data is for a lead-acid deep-cycle battery.

It is to be noted that battery capacity gets lowered for higher discharge currrents.