Thank you all of you for replying. What ought I do to investigate? The battery pack has a big label seal on it. I opened it as far as I could without breaking that seal (just the other side), and the batteries are wrapped in a tough blue shrinkwrap.
There are two sorts of smells. The smell in the room is a non-sweet-smell, just a chemical smell, moderate, quite noticeable when you're used to fresh air, not extreme; smelling the front part of the opened battery pack revealed this smell again, a bit more concentrated. It's an electronics-y smell, like fresh alkaline batteries used to smell. I thought it might be from glue or something else used in manufacture.
The second smell type was from the part of the battery pack which connects to the mounting, there is a slight - slight - smell of rancid almond essence, i.e. sweet. I could smell that with the battery pack closed or opened. But it was only when I pretty much stuck my nose against it, i.e. not the smell affecting the room.
Would this be adequate investigation, and suggest that any leak of the lithium (the sweet bit) was negligible and should be ignored?
I've bought a 1m x 1m fire blanket (good for £4)
http://www.amazon.co.uk/dp/B003RUJFM4/ref=pe_385721_37986871_TE_item to wrap the thing in when not in use, and hopefully will get hold of a new kettle type fully-lidded barbecue with high legs to store it in. That would be adequate, provided that any fire was just a flame and smoke type, and involved no explosive kinetics which could make flame or material escape the barbecue and set fire to anything in the room.
