Usually, if a battery fails to hold charge, it's a defective battery. Perhaps, you got a lemon from your Volvo specialist. To be sure, charge the battery up and disconnect the cables overnight. Then, test voltage the next morning. If it holds charge, it should be >12.2 VDC. If much less, the battery is no good.

If the battery is good, then you have a drain on your system, probably a short circuit somewhere. To isolate, hook up an ammeter in series to one of the battery terminals. If there is a short, you'll get a non-zero reading. To isolate which circuit, pull fuses out one at a time to look for a zero reading. If you get a zero reading from that fuse, then there's a short in that circuit.

From my experience, what you've just changed may be the culprit. So, pay a lot of attention to the charging circuit---alternator.