So many of the tools we utilise in our photography and filmmaking adventures these days are battery-powered. Many of those batteries, whether they’re removable or built-in, are based on lithium-ion technology, which generally doesn’t do well when left for a long time at a near-full or empty charge. Other devices may also use alkaline batteries which can leak when unused for long periods.
For the latter, just go and remove them from the devices. Flash triggers, speedlights, intervalometers and other devices which utilise AA, AAA or other non-rechargeable batteries. Just take them out, and you’re good. For the lithium-ion devices, there’s a little more to it.