The first post asked if it was worth upgrading to the X-4 probe. I would upgrade before I purchased a depth raider. If I had to decided between purchasing a X-4 unit, and a depth raider, I would spend the extra money and purchase the X-4. The x-4 probe uses 4 AA batteries. I put new batteries in mine at the beginning of the season, and change them around the beginning of August. The batteries are not dead when I change them. I sometimes loose signal past 80' around this time when they get weak. This is somewheres around 18 trips on a set of batteries. One of the issues with the 840 probe is that it needed to be turned upside down when not in use. Turning it upside down shuts it off. Too many people put it away without turning it upside down. The X-4 probe has two metal probes that stick out the front. These are used for turning it on and off. When the probe is put in the water, it turns on. You dont have to worry about it not being turned off when out of the water. The electronics on the X-4 probe are sealed in acrylic. There is no way for water to get in with the electronics! There is a double O-ring seal which keeps the water away from the batteries. Notice....I said batteries. The batteries are seperate from the electronics, and there is a connector that connects them to the electronics.