Viano / Vito two battery setup - how might it be connected?

[Droverunner]

I've just bought a 2012 Viano 3.0CDi which was in police service until late last year and then has been largely unused until it was delivered to me on Sat. It started Ok to get off the transporter and I've been working through a major service yesterday and today with inevitable multiple engine starts plus fiddling with elec windows, radio, rear air suspension etc so a fair power drain and no length of time running to re-charge.

I've had a couple of glitchy issues with the central locking today so wondered about battery voltage. I went to what I thought was the only battery... under the drivers seat. Taking a reading from red terminals in the under seat area showed less than 12v so I wondered that it was starting at all but we did then have its first run out. After that went to put it on charge via the under bonnet jump start terminal and found 12.3v there before charging.

Had a bit more of a poke around and was surprised to find a second battery under the passenger seat. And that's as far as I've got tonight and now left on a trickle auto charge until tomorrow am.

Bearing mind this was a police vehicle which may or may not make a difference how on earth might the two batteries be connected and to what? Tomorrow I think I'll have to compare post charge voltage at the underbonnet terminal and then pull both batteries out and test their individual voltages. For a start it is important to know which is the main battery as a Viano is normally supplied.

BTW also going to code read it tomorrow which I haven't done yet.

Any thoughts appreciated.

 

[Blobcat]

Firstly I’d get a battery conditioner and connect it to the main battery to get that back to full health. The age of the battery will be on one of the terminals (week and year code)
There will most likely be a split charge system, that charges the auxiliary battery once the main one is fully charged.

 

[Droverunner]

My charger is a smart type and I've run the trickle output/maintenance cycle overnight. Going to see what that's done and read codes.

Which side seat is the main battery under normally because they are both full size with OE looking connections.?

 

[M80]

Main battery under passenger seat.
It will be interesting to learn how the 'leisure' battery is incorporated into the system. On campers that is often via a battery isolator but expecting plod on surveillance to use that may be too much.

I wonder if yours also has an additional security alarm / immobiliser fitted.

12.3 volts isn't bad, 12.6 would be ideal. With ignition on that voltage will drop.
I would suggest both batteries might benefit from a pulse charge conditioning cycle. I would prefer to do that with batteries out of the mo mo.

Before going on diagnostics I would prefer to see the main battery stabilised and the mo mo run over a few times. Low voltage brings up many confusing codes.
So clearing all codes and just concerning about those that return makes sense, if any do.

 

[Droverunner]

Thanks guys. Main battery was a replacement Varta AGM which even after a 40ml run yesterday in daylight and an overnight charge still read 12.3v off the vehicle.... but it started OK as I said.

Aux battery under drivers set was date coded to just before the reg date of the vehicle and a Mercedes OE AGM. Off the vehicle refuses to take a charge on either of my decent AGM approved battery chargers above 12.1v.

I never skimp on batteries so have ordered a new Varta AGM of a matching capacity which I will make the main one and for now put the so so main battery into the aux posn to replace the virtually dead one. I'll see how that goes.

Agree re code reading on a low battery but I couldn't resist a look. Couple of random canbus codes which I deleted and then just two for open circuit puddle lights which I'll check but assume bulbs gone.

The aux battery and its wiring to some sort of control unit near it is so obviously Merceded OE at build but I have no idea what it feeds.

 

[M80]

It possibly monitors battery voltages and automatically switches charging. I would imagine it's design is to ensure the main battery remains at optimum.

Personally I gave up on AGM batteries some time ago and consider the old fashioned lead acid to be more robust and reliable.

 

[Droverunner]

Fair enough re AGM but it will be better than it is now. I've always got on OK with decent lead/acid.

 

[jimbg]

It would be nice to take advantage of twin batteries with a switch such as this:

Proster Dual Battery Isolator Marine Switch 4 Position 350 Amp 12V Battery Switch: Amazon.co.uk: Car & Motorbike

Buy Proster Dual Battery Isolator Marine Switch 4 Position 350 Amp 12V Battery Switch at Amazon UK. Free delivery on eligible orders.

www.amazon.co.uk

 

[Droverunner]

Ha ha yes... very boaty. However with the second battery's purpose and what it feeds unknown for now I'll just run with one new and one good battery and everything else as is.

 

[AndyHB]

Ha ha yes... very boaty. However with the second battery's purpose and what it feeds unknown for now I'll just run with one new and one good battery and everything else as is.

@Droverunner we're in a similar position with our recently purchased 2008 Viano, how did you get on?

 

[Droverunner]

Do you mean as in a few glitches on a vehicle that's been standing or a mystery second battery?

Anyway I established my main battery was under the passenger seat and fitted a new one. The OKish old main one was transferred to replace the near dead secondary under the drivers seat. All odd electrical glitches have gone with the new battery and regular use.

Over a couple of investigations I've established my secondary battery is fully plumbed in as fitted new at the factory in respect of input cabling and a split charge relay. But anything it did feed wasn't part of the main vehicle electrics and has since been removed. There was police radio, phone charging and other equipment fitted under the rear voids below both front seats and together with extra interior lighting I think this is all the gear stripped out/disconnected together with any wiring all the way back to the battery.

So no the battery doesn't feed anything. now. The extra LED lighting is still in place throughout the front and rear so at some point I'll reinstate the wiring to them from the Aux battery, also I will feed one of my four "cigar lighter" style 12v sockets from the Aux battery as one that could be used for a long period with the engine off and not spoil starting.

Images... main battery location... main battery area wiring... aux battery wiring.

 

[AndyHB]

I have had a poke around under the seats of the Viano and found that there is probably room for a 2nd battery alongside the first under the passenger seat and i believe that there's enough space for a battery under the driver seat so i could be quids in. I do wonder about installing a second battery with a split charger but can't see how it would be used by the rest of the van without leaving the ignition on.

Let me know if i'm wandering into thread hi-jacking territory.....