That is a very bad idea, far better to add a high quality inverter to make the AC power.

Search for a 12v to 230v inverter?

Thank you for the reply. I already have a really good quality inverter, but would prefer to run at 12v 

The Sonos will run at voltages near to 12v, so it seems daft to take 12v upto 230v and then back down again. 

A DIY self repair discussion suggests that primary step down is to 24V. This implies that you would need a step up inverter for your 12V source.

Look at some teardown videos and decide if you really want to try and work inside your Sonos.

A good inverter is going to be a out 90% efficient and safe,plus it won't kill your Sonos if it glitches.

Its as much convenience as anything else, everything else on the day to day running of the boat is 12V, so turning on the inverter every time we play music or put the TV on, will be a slight pain. 

If I can find the voltage the Beam runs at and find a suitable regulated power supply, it makes every thing easier. 

I think the bottom line will be which device is easier for you to modify for remote power-up — an inverter or the SONOS. 

What is your overall concern? Space? Wiring clutter? Power consumption? Operator convenience?

There are a few considerations. 

Convenience is the biggest one. 

I would need to cabe 230v to the area as well as 12v using the inverter. Using 12v would only require one feed, so cost is probably neutral. 

It just depends on how easy it is to modify and power the Beam from 12v, that's why I've asked on here, before I go stripping my Beam, to see how it's done. 

What about a decent rechargeable Bluetooth soundbar? I hear they exist.

Why the need for cabling 230v as well as 12v?

I like the Beam, if I went for a Bluetooth option I would get the Roam 2, but prefer the Beam form factor. 

If the Sonos was 230v, the TV and everything else is 12v . 

Which power source is more convenient to run to the area? It makes sense to run only one power source. If you run 230V to the area you’re done in the BEAM area. If you run 12V you’ll need to find space near the BEAM for the inverter and any control devices. How are you powering the TV?

Are you using any Voice control? If so, you could pretend that the 230V is a fan.