D Batteries

My pathway lighting and video monitors take D cell batteries, I've gone through 2 complete sets in less than 12 months. Each pathway light takes 4 D cell batteries at a cost of $16.84 each light. That's $67.36, then add the 2 motion video monitors batteries. Now, I need to replace the batteries again! I've adjusted the motion sensors and repositioned everything. Unfortunately I can't afford this many replacement batteries. The lights and monitors are installed and not useable.