V50 battery
 

Can i disconnect the battery to fit a new one without provoking any electrical issues? Is there a time limit before everything locks out or the car dissolves into the ether?
55plate (06) v50 2.0d
Procedure?

You can fit a new battery without issues. However, the official instructions include telling the CEM (central electronics module) that you've fitted a new battery so it can adapt the charge pattern to it. You can do that yourself with Vida/Dice or have someone do it for you.

You need a 10mm socket and an extension for your ratchet wrench. A large straight-edged screw driver is recommended to help open two plastic clip retainers.

Procedure is:
Remove top of battery tray
Disconnect the (-) cable at the far end of the battery by loosening the 10mm bolt, you don't need to remove the bolt completely. Yank the connector off, it may spark as you remove the cable and this is normal.
Disconnect the (+) connection at the near end of the battery (that's the one made out of metal)
Follow the red cables down the front of the battery box and unclip the two retainers holding them
The front and sides of the battery box is one piece, remove it by gently prying it from the rear part of the box. You can see where the parts fit together at the top of the box.
Unbolt the battery retainer clip from the bottom of the box
Lift the battery up and out. Do not tilt it more than 25-30 degrees or you risk spilling battery acid
Install new battery in reverse order, finishing with reattaching the (-) cable. Tighten the bolts so they are good and tight, don't overdo it. Use a permanent marker and write the date of installation on top of the battery.

I've left the battery out of my car for several hours while working on it with no negative side-effects after reconnecting the battery, so I wouldn't worry about that.

/Teddy

OK thanx for that, I can manage that OK, so if I don't have a vida/dice or someone to set it up for me can I just go ahead and change the battery and hope and pray that everything will work or is it critical that a reset is done? Or am I wasting my time and money? I've been advised my static battery v is too high @12.84v which can throw all sorts of elec issues, the charge voltage is fine @14.40 and stable, battery is only 2yr old, and under test reads healthy.
Is 12.84v too high or is it bull####?
At the mo it's my cheapest option to try solve elec issues with this gremlin of a car which I am slowly losing the will to live with sadly.

12.84V seem more than normal, mine show 12.5 after car not being used for a while but i dont think its the issue, would be worried about gremlins if battery was showing 12.1 or less... Replaced my 7y old battery when was dropping to 12 and below (and electric issues started to show) but in your case i dont think its reason to worry... also you have presumably diesel battery maybe those have higher static voltage than others?

2.0D models shouldnt have issues with disconnected batteries, only 1.6D if i remember correctly can loose key code etc, dont think 2.0 has the same issue.

It isn't super critical that a reset is done, however it will prolong the battery life when done because the way the battery is charged changes based on how old the CEM believes it is. The older the battery, the more it is pulse charged to keep it healthy.

The brand new Varta battery in my 2.0D shows 12.57 volts in standby, while it fluctuates up and down with a max reading of 13.04 volts when the canbus is active (doors unlocked) and engine is off.

Like LOB, I wouldn't worry about a reading of 12.84 volts from the battery. The electronics in the car are rated to sustain voltages of 14.5 volts so they should be fine.

The CEM is notoriously vulnerable to corrosion either in the plugs or internally, although I'm sadly no expert so I can't offer any firm advice on what you should do from here to address the issues you're facing.

If you want to check the battery voltage at rest, so no engine running and everything turned off, you should do it only when the vehicle has not been used for at least a couple of hours but ideally overnight. If you measure the voltage soon after the ignition is turned off then it will show a reading that can be higher than expected.

A perfectly good car battery should be at 12.6 volts or above at rest. The air temperature is important as the battery voltage will decrease as it gets colder so bear that in mind when measuring the voltage in the middle of winter.

With the engine running at a fast idle or above the voltage should increase to between 13.5 and 14.7 volts.

Unless you are using a calibrated instrument, and using it at its calibrated temperature, I would not expect to get highly accurate results. Most cheap multi-meters can be 0.1 or 0.2 volts out so your reading of 12.84 may actually be 12.64 anyway.

As others have pointed out, at 12.84 volts it shouldn't be causing any problems as the system voltage will more than 1 volt higher once the engine is running. A lot of electrical problems stem from bad connections so a good place to start is to look for those.

Corrosion from water ingress is another common cause of electrical faults. Just don't ask me how I know that...

no problem changing a battery , nothing you need do . Some of the earlier models would loose their immobiliser codes if the Engine ECU was left without a supply for a few days ... a reload of the software by volvo would bring it back to life , this is only applicable to the 2.0 D engine , Volvo engines dont do this .

So reading on through various forums it seems the CEM is the place to start from, I've read a lot about corroded/dirty terminals causing some of these issues on the v50/Ford focus.
So whilst I've got the got the battery disconnected it would be a good time to inspect a clean the contacts wouldn't it? Or would this open up a whole new can of worms?
Voltage check on battery again this morn after not being used for 24hrs and left unlocked 12.72 so I reckon that passes the test.
Has anyone changed a SWM/clock spring? As I think it's my next step if the CEM clean up proves fruitless.
The car has 180k and is the PSA lump but we like it and it pulls our caravan effortlessly, mechanically we've had no issues but these electric gremlins are making me wonder if I'm throwing good money at bad rubbish, I'm not in a position to pay dealership rates on a car that is worth prob not a lot.

If the CEM has communication errors the fix is 3 pairs of network repair terminals from Volvo they are improved . Otherwise you will be "cleaning" the terminals every 6 months , they don't get dirty it is the fact that they "fret" so wearing off the tin coating .