current draw effects on battery life
Assuming that's an SLA, see a typical Data Sheet. But that's for a good-quality battery.

See also Calculating the Battery Runtime

At such a low current you should get close to the nominal capacity. So 7/0.008 = 875 hours or 36 days. Subtract some time for self-discharge depending on ambient temperature.

That assumes your 8 mA is what the regulator draws from the 12V side.