Hi Jim, the coil should hold a charge for about 12 hours. Mine is at about 6 hours. If you run the standard coil on a lower frequency it will drain the battery faster. From what I read, some people have had the deus for 3-5 years before a battery change.
I've had mine for 2 1/2 years. My average hunt is about 5 hours long but when I go on a group hunt I need to charge my battery in the field. It's just annoying to have to wait on it. Don't get me wrong, I love this machine! I just wish I could find a website that wasn't in a foreign language that sells the replacement kit.
Scott in NKy