Battery stash can’s are a genius way to conceal small valuables and cash. Batteries can be loose in luggage and not look suspicious. They can also be stored inside other devices to even better avoid detection. If you go this route, be sure to use the batteries in low value items to lower the probability of the device and the battery getting stolen.
These are best used when you’re very conscious about the battery and not long term storage. A single battery that doesn’t have a charge is easily thrown out by someone not in on the secret. Keep an eye on your goods!