What is the battery level shown in the App just before you remove the Roam from the charger …and also after it powers off and is then returned to the charger and powers on again.

What’s the power output (not input) of your USB charger in volts/amps? It should be stated on the charger.

When I unplug it’s about 85%. Looks like the usb charger is 12w. Looked this morning after it’s been unplugged all night and it’s 37% although I haven’t used it at all overnight. 
 

Ideally the charger needs to be a power output of 5v at somewhere between 2 or 3 amps … I personally use 5v/3A power output, which takes about 2hrs 15mins (approx.) to charge the Roam from empty to 100%.

From full charge the device should then play for at least 10 hours at 50% volume. It fall’s asleep after 30mins inactivity and will wake up when you either press the rear power button or simply open the S2 Sonos App on the same network.

I ‘suspect’ your charger maybe a little under-powered and therefore taking a long time to bring your device up-to it’s full charge (perhaps?). 

Thank you! Yes I see what you mean. It is 5v. I think the falling asleep thing makes sense, although odd if it doesn’t count playing something as activity. I often listen to the radio and don’t touch the device for 30 mins. Is this right that it would sleep in this case?

Also do you know anything about it not working when it’s off wifi? Am I doing something wrong?

No if the Roam is playing it should not sleep nor stop working off it’s charger - it still sounds like an underpowered charger to me - 5v but at what amps? - if it’s a typical phone charger at 1A then it’s not producing enough charge to keep the battery going.