I’ve been having an issue with my 2000 Honda Civic where the battery drains itself to dead when it sits for too long. Seems the alternator is working because once I jump it, it drives fine and will start up again with no issues within a several hour period.(also depends how long I drove). I don’t believe there’s any parasitic draw because the only thing I’m aware is taking power is the display on the radio that shows the time. Otherwise, headlights are off, radio is off, nothing plugged into the lighter socket. I just replaced my old battery for this reason now the new one is doing the same, though I did accidentally drain it once leaving the headlights on. I’m unsure what to do. What could cause this?
It could be a couple of things. A parasitic draw or a bad replacement battery, or both. On simple test would be to disconnect the battery after parking it and after it sits for enough time to normally pull the battery down, then reconnect the battery and see if it starts normally. If it starts okay, then you have a parasitic draw. If it does not, you have a battery or charge system problem. It’s also worth noting that running the battery down multiple times is a good way to ruin a new/good battery.