Yes, it is perfectly fine to leave a Battery Tender on all the time. In fact, many people find that it is the best way to keep their batteries charged and ready to go. There are a few things to keep in mind, however, when using a Battery Tender. First, make sure that the tender is designed for the type of battery you have. Second, check the manufacturer's instructions to see how often the unit needs to be replaced. Finally, be sure to unplug the unit when not in use so that it does not overcharge your battery.