In my area we fly year round between rain storms. Our clear Winter days can be down in the 20-30F range quite often. Most planes I fly wouldn't be too much of a concern if a battery went too flat and I had to land dead stick (other than it is hard on the batteries). However, I am currently working through the process of learning to fly a twin and it won't really fly dead stick or power reduced (to a point).
My question is: For fairly new batteries (less than two years) how much should the flying time be dialed back to avoid over-discharging the batteries or worse having to land dead stick or with too little reserve power?