I replaced my battery a couple weeks ago and have been having problems weak starting ever since. The battery was 7 years old so I figured it was toast when my car failed to start. I know that my alternator is putting out 14.0 -> 14.2 voltages while my car is running because the onboard computer tells me that much. I've tested with lights radio ac blinkers on and it still maintains 14.x volts with the car running I took the battery to auto zone (where I got the new battery) and they load tested itbattery and it tested fine (after it was charged). After they charged up the battery to full it did not start weak at all but after letting the car sit for a couple days the problem came back. So I am thinking bad alternator diode or some other source of parasitic drain. I don't have tools but will get them if an alternator change is in order.