I believe It's less stress on the battery to recharge at 50% than it is to go down to 20%. By that reasoning, I recharge most of my batteries after every ride. If you want to maintain longevity then, recharge your battery to 80% after each ride, and top it off at 100% just before you ride it again.
80% is 40V on your 36V14.5 AH battery. A subsequent 60-90 minute charge with a 2A charger will put 2-3AH into your pack, which is about the missing 20% to get it full.
Without an 80% charger, it sure gets complicated, I have a Luna 80/90/100 52V charger, so I can leave my 52V packs at 90%. I don't use them that much. However, my 36V and 48V batteries get used daily, so I simply recharge them after every ride,
By the way, in your other thread you said Luna claims their charger only runs on 110VAC. Wow, they must be taking different stuff than coffee on their breaks again, I have a Luna 80/90/100 52V charger, It clearly states 110-240. Universal switching supplies always run on 110-240. It's globalization.