After joyously owning my Mk5 since days before the NZ lockdown of 2020, I encountered the issue of a flat battery a few days before Christmas. Fantastic timing given so many businesses closed early this past week, with many of them not being available until January.
With everyone being closed I started with the diagnostic process myself. The battery has an indicator glass that should go green if the battery has failed, it remains black. Check voltage on battery connected to the car, it sits at around 10.5VDC, disconnect from the terminals this steadily climbs to 12.3VDC in a few minutes. So last night I disconnected the battery and placed it on a newly purchased 'automatic' 4A 8-Stage charger overnight. This morning I disconnected charger and voltage is only sitting at 12.3VDC.
Using a jump starter box I checked for drain sourced in the car and learned that there's a resting draw of 95mA. Remove relay A1 in the engine compartment and this drops to zero. Voltage drop checks show a value of 2.3mV across F12 is the kick plate fuse box, door control mules(?).
After running those checks I went and checked the still disconnected battery and found the voltage had dropped further. I suspect despite the indicator glass, I have a faulty battery. Perhaps in conjunction with the current leak. The battery age is at least 4-years, there's a Japanese service sticker noting a '16 date.
Now the conundrum, What should the battery spec be? Some sites suggest it must be 'calcium' (which makes sense as most modern batteries are) yet others insist that it should also be AGM. And this is where I am stuck, as there are availability and price differences.
The battery that is in the car has a part number 000 915 105 DG or Exide TU3. Ratings are 72Ah/380A and then 640 EN. No where does it mention this is an original nor whether it's AGM or not.
