How to know when you've reached enough resistance for a battery?
A 1hr discharge is safe so Vbat/mAh=R but  at this current the 20 hr ___ mA rate may only be 50% for alkaline and 75% for Lithium (ballpark.) Where [watts] P =V^2/R, so as you reduce R and increase V/R=I[Amps] the self heating raises the battery temperature. If warm only after a few minutes, it's OK.but if it gets warm in seconds, not OK. –

Thus a 2Ah AA battery @ 1.5V can support 1.5/2= 0.75 Ohm for 30 minutes maybe.. check datasheet