You may want to try using Li Ion batteries, they have a much better voltage discharge curve and last much longer than alkaline batteries.
E.g.
https://www.amazon.com/Energizer-Lithium-1-5V-Energy-Battery/dp/B001INHELQ
NOTE These are NOT rechargeable batteries, do NOT try to recharge them as they may explode if you do so. These are one use and throw like Alkaline batteries. See this post for more details on Li Ion vs Alkaline.