Devices in storage fail in ways that have nothing to do with how they were used.
Take the batteries out
Alkaline cells leak over years, and the leak corrodes contacts and often kills the device. A remote, a camera or a handheld console left with batteries in a drawer is the most common way a working item becomes scrap.
For a device with a built-in lithium battery, store it part-charged rather than empty or full, and give it a charge every few months. A lithium cell left completely flat for a year may never come back.
What else destroys them
Humidity, which corrodes contacts and connectors. Heat, which ages batteries and capacitors faster than use does. Dust, in fans, ports and optical drives. Static, for bare boards and components.
What to do instead
- Dry, with silica in the box, away from an outside wall
- Cool — never a loft, never on top of a cupboard under a hot ceiling
- Dust out, ports covered, cables coiled loosely rather than tightly bent
- Bare components in anti-static bags, always
- Not sealed in plastic with no desiccant, which traps whatever humidity was in the room
Before storing anything you may sell later
Sign out of every account and remove the device from your account while you still remember the password. Future you will be grateful, and a locked device is nearly worthless. Selling electronics.
What it costs
A box, silica and ten minutes.
Questions people ask
What if a battery has already leaked?
Do not post it. Many carriers refuse damaged cells, and the device may be beyond help.
Should I charge a stored laptop?
Every few months, to part charge.
Is a loft acceptable?
No. Heat is the main enemy here.
More: describing condition, common mistakes.