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Background: I know nothing about cars but had my battery replaced just now and learned that you need to reprogram the onboard computer after changing the battery [1]. This is for a 2012 VW Passat if it matters. In my case I switched from a standard flood filled battery to an AGM but both were 12 V. I can understand reprogramming the computer if one were changing the battery with a different voltage rating but does it really matter if you are just changing from standard to AGM and why? What difference does it make? I mean as far as the car is concerned it is still connected to a 12V power source.

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Are you confusing radio memory presets lost after battery disconnect, requiring programming them after battery replacement?

Engine computers don't require programming when a battery dies during winter starting or when replacing it. However, there is live memory related to emissions systems that reset when battery power is removed; driving automatically lets the emissions system learn new parameters. As long as the check engine light was off before battery replacement, it should remain off after a new battery is installed, regardless of type of battery (flooded, AGM, sealed maintenance free, etc). Enjoy driving with your new battery for a few years of trouble free starting as long as periodic engine maintenance is performed; air/oil filters, coolant top off/replacement, spark plugs, etc.Your owner's manual has info on maintenance. If no manual, some manufacturers offer pdfs online.

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  • to answer your question - No. Please see the linked video for what I mean.
    – morpheus
    Commented Jun 21 at 16:05
  • Well, since you already replaced the battery, the youtube video suggests VW instrument panel indicators should turn on and remain on. Every vehicle with electronics; when turning ignition On, perform powerup self tests, cycling their indicators on, when self tests pass, turns off indicators. Electronic modules performing their own self tests; ecm, bcm tcm, abs, entertainment system, tpms, etc. When each passes, the only indicators left on before starting; park brake, battery, oil and seat belt. If your car starts and runs, where's the problem? Call VW for advice If I'm mistaken.
    – F Dryer
    Commented Jun 21 at 18:53

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