T5 Van Secondary Battery

[Rebuild]

Looks like the standard fitment secondary battery under the drivers seat, is toast.Only been 10 years
Mine is a sealed Delkor Calcium 55AH, 550CCA

If the second battery is bad, will this drag the main battery down? Second currently reads 10.35V, main 12.3V
Would i be better off with a deep cycle as a replacement for it? Or do i go a regular sealed starting/high CCA type?
What are these used for? Are they a backup to the starting battery?

Any other requirements?

(i did do a quick search, couldn't find anything useful)

[Bryn23]

There is a little bit about the 2nd Battery in the FAQ thread T5 FAQ and How to THREAD (up to August 2009).

The only thing that should be running off a House battery should be Aux...and it should be isolated from the main battery.

So i would be looking at a Deep Cycle AGM, you should be able to fit a 68ah up to a 100amp AGM under the Drivers seat.

Although, i was under the impression that factory 2nd Batteries were under the Passenger seat?

Someone else will know more than me...

Got to be happy with 10 years out of a battery.

[Rebuild]

i think 2nd battery under passenger seat was standard for Multivans/Camper types. Mine's just a Panel van.
I thought it ran the alarm/central locking,etc, although when i disconnected it, central locking still worked.
There was no current flow with ignition off on the +ve line either, so it wasn't drawing/draining anything
I'm a bit size limited under there too. 280Lx170Wx190H - ish

[Rebuild]

I've taken the 2nd battery out(for anyone else, remove seat 2x M10 XZN and 2x13mm Hex) and the box it sits in doesn't look like a quality VW fitment(self tappers through the floor for the battery hold-downs for a start).The convenience unit is screwed to the plastic sides of the box too.
Thinking of going a Supercharge Allrounder 60AH 550CCA which is a combo cranking/deep cycle type.Had a good run on a Supercharge battery many years back

[Leespe]

100 ah fits under the seat ok