Most Wi-Fi devices just don’t have very good battery life. 
Schlage says the encode is expected to last six months on one set of batteries (as opposed to their Z wave and Zigbee locks which are expected to last 12 months), but yours is obviously worse than that. I do know quite a few people who are only getting four months out of one set of batteries with that model, although those are fairly busy households.
Schlage suggests that the most frequent reason for excessive battery use is that the Wi-Fi connection to the lock is too weak and it is having to send multiple connection requests. So you might check Wi-Fi strength in that area.
If that doesn’t fix it, I would try contacting Schlage support and see if they have any suggestions.