Battery issue when left for a week
 

Hi, the last two times I’ve been on holiday and left my car at the airport the battery has been flat on my return. It is fine all year long until it is left for a week. I’ve had the car to Halfords a few days ago and they struggled to get a reading on their machine. First they connected under the bonnet and got a fault, then we removed the battery cover and they did it again. Not actually
Sure if the test was carried out correctly but the result was 540cca and they told me therefore the battery was good. Do you think this is correct and do any of you have a suggestion please? It is a S3 013 Bosch Car Battery 12V 90Ah Type 019 S3013 and is 3.5 years old on a 2007 Xc90.
Thanks in advance everyone, you’ve always been helpful before.

Firstly, correct battery size depends on engine type - what do you have?

Here are the battery specs from your Owners Manual:

Engine 2.5T
Cold start capacity (CCA) 600 (800A if parking heater fitted)
Reserve capacity (RC) 120 min
Capacity (Ah) 70

Engine 3.2
Cold start capacity (CCA) 520 (800A if parking heater fitted)
Reserve capacity (RC) 100 min
Capacity (Ah) 60

Engine V8
Cold start capacity (CCA) 600 (800A if parking heater fitted)
Reserve capacity (RC) 125 min
Capacity (Ah) 70

Engine D5
Cold start capacity (CCA) 800
Reserve capacity (RC) 150 min
Capacity (Ah) 90

The Bosch Car Battery 12V 90Ah Type 019 S3013 is rated at:
Cold start capacity (CCA) 720A
Capacity (Ah) 90

If you have a D5 engine, you can see that the battery is slightly underrated for your car: it delivers 720 CCA instead of 800 CCA.

If Halfords correctly measured the battery at 540 CCA, then it is currently at 75% of it's original CCA capacity (540/720 = 0.75)

HOWEVER it is unlikely that that is your problem, as a battery at 75% CCA should still start the engine.
You need to check for anything that is not switching off properly (cabin lights, glovebox lights) and then check for parasitic drain when the vehicle is in full sleep mode.

Thanks for that! I always thought that the seller might have put a slightly lower capacity battery in the vehicle. How do I check for parasitic drain? Multimeter on the terminals with everything turned off?

There are two measures of a battery - it's power delivery (measured in cold cranking amps - CCA) this is how much power it can deliver in an instant.

Then the storage capacity (measured in Ampere Hours - Ah) this is how much electricity it can store.

Think of a bucket of water - the CCA is how fast you can pour water out of the bucket and the Ah is how much water the bucket can hold.

When modern batteries degrade it is usually the capacity that is lost at a greater rate than CCA, and older batteries can "self discharge" - so to make a judgement on the CCA reading is not conclusive by any means.

FYI I had the same problem and it was cured with a new battery. Volvo dealers are quite competitive for similar quality batteries available elsewhere.

If you do test with a multi meter you need to lock the car and leave it for a minute for the audio, courtesy light etc. to shut down.

Here's a good read about checking standby current.

In a nutshell

- It may take up yo 10 minutes for the vehicle to enter sleep mode (with all doors locked, etc.)

- The total standby current should be less 25 mA



And for those keen readers, the whole VIDA wisdom (applies to 2007 V8)

372: Checking standby current
Checking standby current
Preparations for standby current measurement General
When the vehicle sets the communication buses and the control modules in "sleep mode", power consumption drops. Factors such as whether the vehicle is locked, the alarm is on or off or whether any doors are open affect the rate at which the vehicle will reach standby power consumption. The lowest power consumption is achieved the quickest when the vehicle is locked, the alarm is on and the vehicle's doors are closed.
Preparations
Ensure that all lighting is switched off.
Ensure that the diagnostic tool is not connected in the vehicle.
Open the tailgate or trunk lid and bonnet and set the locks to the deadlocked position using a screwdriver for example.
Open the driver's and passenger doors and set the locks to the deadlocked position using a screwdriver for example.
Close the rear doors, remove the key and lock and alarm the vehicle. Never use reduced alarm as it then takes longer for the CAN network to continue in "sleep mode".
Wait until the vehicle has come down in standby current consumption, which can take up to 10 minutes.
Note! Do not open any doors or the test will have to be restarted from the beginning.
Checking standby current
Connecting the measuring instrument General
When measuring the power consumption, it will soon become evident if there is a power consuming component in the car drawing an excessive amount of the battery capacity. If it is clear that the power consumption is greater than the specified limit values, fault trace by successive elimination.
The method for measuring the total standby current consumption is described below.

The vehicle's standby current is measured using a multimeter.
Note! If the vehicle has been run to operating temperature, check that the system relay has been activated. An activated system relay causes increased standby current consumption. This is normal under certain circumstances.
Measurement method
When measuring the vehicle's total power consumption, connect the measuring instrument in series with the battery at the battery's negative pole.
Connecting the multimeter at the battery negative pole
Note! To avoid current surges that could damage the measuring instrument when the battery cable is connected, carry out the following. Never connect the measuring instrument if the engine cooling fan is in operation as this can damage the instrument.
Ensure that the multimeter is equipped with a clamp and a probe.
Check that the multimeter is set for current measurement.
Disconnect the nut on the battery cable's negative pole.
Note! Do not lift the battery cable so that the circuit is broken.
Secure the clamp on the negative pole's battery cable terminal.
Note! Check that the connections are installed correctly. If the circuit is broken, the standby current must be re-checked from the beginning
Place the end of the probe on the battery's negative pole.
Slowly lift the battery negative cable without removing the probe.
Stop when the battery negative cable hangs freely without touching the battery or the probe.
Measuring and reading off the total standby current.
Read off the standby current consumption. The total standby current should be less 25 mA.
Note! If the car is equipped with "Volvo on call" and the standby current is too high, wait 5 minutes and measure again. The "Volvo on call" system is active for short periods and then increases the short-term standby current above the normal value.
Reinstall the battery's negative cable.
Look and listen for unusual vehicle behaviour. Check, for example, if a relay is hot, if it is this can indicate that current is flowing through it.
Note! Do not carry out work inside a vehicle equipped with mass movement sensors as the alarm may be triggered.
Check that the CAN network has continued in "sleep mode", see instructions. Checking Can-net's rest status
If the standby current is OK and the CAN network is still in "sleep mode", reset the vehicle.

Sorry if it's a silly question but you don't leave anything plugged into the rear cigarette lighter do you as that is always live?

I bought one of these which will cut off power to anything once the voltage hits a certain level which you can configure:

https://www.amazon.co.uk/gp/product/B0785D3GYB

My 2004 XC90 has still the original (14 years) battery. It was measured that it effectively around 30% of the original capacity (or whatever measure it was) and it was fine after 2 weeks holidays in December.