What high quality accurate gauge or meter have people added to their 12V deep cycle battery used to run their fish house stuff? I don't recharge mine with a generator or any solar stuff, so I'd like to be able to quick glance at something and know it's about time to take it in at the end of the night to start over. What is the gauge or meter really telling you about? Is it the voltage or amperage? I have a regular amp/volt meter. Is it as simple as taking a quick voltage reading at the end of the night, and then knowing what the minimum # is to trigger a recharge? Before you start harming the battery? I've seen the dial/gauge type and also a digital readout type online so far.