[Tannaton]

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.