VW T6 Starter Battery Upgrade: Fitting a Larger 96Ah AGM and Recoding It

The Problem

The original Moll 70Ah EFB battery was failing to hold charge after several days sitting unused, causing no-start conditions. The owner wanted to fit a larger AGM battery but was unsure whether it would physically fit and whether the van's ECU needed recoding.

Solution

1. Turn the ignition off, then disconnect the negative terminal followed by the positive terminal from the old battery and remove the hold-down clamp.

2. Disconnect the main wire from the fuse and distribution box that sits on top of the battery tray and move it to one side — this is the only clearance needed to fit a larger battery.

   • If your van has no top-mounted fusebox (e.g. Startline trim), skip this step.

3. Lift the new AGM battery into the engine bay, rest it temporarily on the panel bar to the left of the headlight, then tilt it down into the battery tray and secure the hold-down clamp.

   • The T6 uses a Type 110 (H8/LN5) battery footprint. A 96Ah AGM in this size is typically a Varta H8 / Bosch S5 A11 (AGM) class unit — confirm the exact length, width, height and terminal layout against your tray before ordering (verify part number and case dimensions before ordering).

4. Reconnect the positive terminal then the negative terminal.

5. Code the replacement battery into the van so the charging system recognises it as a larger AGM rather than the old EFB:

   • VCDS: Connect, then select controller [19] – CAN Gateway. Open the Adaptation function and edit the battery channels — set the battery capacity (Ah), the manufacturer/brand code, and enter the new battery's serial number. Save each channel after changing it (confirm the channel names match your control module software level — they can vary slightly between T6 and T6.1).
   • Carista: With an active subscription, choose your vehicle, open the battery/charging section and use the "Register new battery" function. Set the battery type from EFB to AGM and enter the new capacity. (confirm this applies to your T6 generation before relying on it.)
   • This step is required on stop-start-equipped vans so the alternator applies the correct AGM charge profile rather than the EFB profile.