Control the output current of battery
The DC-DC will only output the current required to maintain 3.3v and nothing more. If your load is 100mA then only 100mA will be sourced from the battery regardless of the capacity of the cells. You should consider though that 81aH is a very large amount and this many batteries in parallel likely has the capability to output a considerable current if something were to malfunction with your load or DC-DC converter. Although not required for normal operation a sizeable fuse connected between the battery and the DC-DC will provide some peace of mind and safety if anything does go wrong.