I use to believe it was due to batteries being recycled over and over so lower quality. But I agree that parasitic drain and short trips are probably the culprit. Then my spouses vehicle is a hybrid so the 12vt is only charging when the ICE is running. Driving even less lately, I've begun trickle charging every 2 or 3 weeks with a battery tender.New batteries all seem to be trash. I think modern cars tend to kill batteries, too. Lots of offline drain and unless you take a long trip regularly you'll never fully recharge it.