The 5 major things that can degrade electronics are electromagnetism, corrosion, excessive temperatures, vibration, and impact.

Electromagnetism is your number-one risk. It only takes a static shock with 1/2 the amperage it requires to make a visible spark to damage data; also, background EM radiation can degrade data slowly over time. Forensics investigators will often mitigate this risk by putting evidence into a static resistant evidence bag, which can then be placed in a faraday bag escentially blocking out all external EM influence.

The second risk is corrosion. For a device that you are not regularly handling, the only major outside corrosive agent you need to worry about is humidity. An air-tight evidence bag also works well for protecting against this; however, an off the shelf evidence bag may not be rated for 500 years. You would likely need to consult with a polymers expert to design such a bag. Vacuum sealing the bag might be worthwhile, but probably not necessary since the small amount of water vapor locked in the bag will expend itself over time doing negligible corrosion. Batteries (as other answers have pointed out) introduce corrosive elements from within; so, they will need to be drained, stored separately, and possibly rebuilt prior to use.

Excessive heat and cold become the hardest part to control over a 500 year gap. You can not exactly rely on an air conditioning system to be maintained for that long, but if you were to store your device in an underground bunker at a depth of at least 30 feet, mother nature will keep your temperature more or less constant for you.

Vibration mostly just affects things with moving disk drives in them; so, for purposes of preservation, I'm assuming you are talking about stored and not actively used hardware; so, this should be a minimal issue. That said, if you are occasionally powering your device on, it is best to do so on a heavy well secured desk or shelf. Lighter desks/shelves can be vibrated by a computer's fans reducing a computer drive's expected life-time by up to 75%.

Last is impact. If you are storing this device in a room full of engineers going about their daily businesses, eventually someone will knock it off the shelf and break it; so, storing it in a place with very limited human access is also pretty important. This makes keeping an electronic device from breaking within 500 years almost impossible for something that you need to use, but if you're talking about purely storage, you should be able to do this and the above 4 steps and have a pretty good success rate at storing electronics for that long.

In response to Edit #1:

If you are talking about a museum scenario, the mostly likely case would be to copy the data onto a replica, then put the replica on display. Museums rarely put items that fragile and rare on display.

TL;DR You cannot.

You need purpose-built items, with specially designed components and maybe even ad hoc designs (PSUs without electrolytic capacitors, etc.), capable of withstanding extreme cold.

Otherwise, there are several chemo-physical processes that would require to be halted.

• Batteries: batteries will degrade over time, and be the first to go. You might want to store the specifications for the required voltage and just hook up a new battery whenever needed.


• Static memories and hard disks: temperature, background radiation and charge loss are all enemies. You can cool down the apparatuses as far as possible, and shield them. Even so, they'll need to be reactivated and "refreshed" periodically. This is, on a longer timescale, what happens orders of magnitude times faster with DRAMs. Otherwise, the iPad won't boot up, because it no longer remembers how.


• Welds. Most electronics being built today will die within fifty years at ambient temperature and pressure, due to the little-known fact that solder islands on circuit boards no longer contain lead or antimony, two poisonous metals that are nonetheless among the few cheap things that can prevent (rather, delay) the formation of metal whiskers. Nickel or gold-plated finishings aren't available on market electronics (some sailors might be familiar with the "brass fluff" growing out of cheap zinc-plated irons. On a much smaller scale, this is the same thing).


• Condenser decay. This afflicts electrolytic capacitors, due to aluminum dioxide breakdown. Extreme cold will delay this process as well as it delays whiskering, but only up to a point - and some components cannot take extreme cold.


• Insulator decay. Several rubbers and plastic insulating compounds are mixed with volatile plasticizers, where "volatile" means that they won't evaporate or significantly run off in fifty or sixty years... but the risk is there and I wouldn't bet on their seeing their hundredth birthday.

Most components aren't engineered to last at all, because the manufacturers know that the items will be replaced anyway inside, at most, of ten years. Just like ol' Henry Ford, who was said to send forensic teams in junkyards to tell him which parts of his cars had not failed so that he could start manufacturing them with cheaper tolerances. Only, this "controlled obsolescence" makes good business sense, and is actually done.

If powered down, electronics can last as long as they don't take physical harm, with the exception of batteries and the bearings in moving parts like fans or platter hard drives.

Batteries, sad to say, can't be made to last that long -- or at least the kind that are useful for portable devices like tablets,. notebooks, and smart phones. There's a type of rechargeable battery that has been shown to last a century, and can likely last much longer than that -- the Edison iron battery -- but they have rather poor energy density. In English, that means a battery that can run a tablet for four or five hours continuously is closer in size to a car battery than the little lithium wafer cells our tablets have now.

Nothing would keep those devices from working on external power, however, so it might be worth storing dry-charged lead-acid batteries, which can last indefinitely before filling with acid.

In all honesty, electronics are incredibly difficult to preserve, due to the very nature of their components.

Particularly, batteries have a defined shelf life, even when unused. Capacitors and resistors (key components in most electronics) also have a limited lifespan, though they may degrade much more slowly if not in use. Storage media (such as flash memory or hard disks) have a limited life cycle related to the number of read/write operations performed. To have the electronics active, even just displaying a static screen, would likely severely limit the lifespan of any electronic device.

The solution for museum displays would necessarily be restoration/periodic repair. There would have to exist a manufacturing process to produce replacement parts for the duration of the displays existence in the museum.

Preserving electronics for 500 years in working order dictates that they not be used at all in that 500 years.

Copper, in particular, gets brittle as current passes through it and it heats up, and the copper traces in circuit boards even more so. The resistance of the copper joints also goes up.

Electromigration is also a problem.

Unfortunately, the only way you will know if they still work is to turn them on, but every time you turn them on, you increase the chances that next time they will not work.

Breaking the device down on a part-by-part basis, and looking at what would be involved in preserving them:

• Integrated circuits: as far as we know, an unpowered integrated circuit in a controlled environment will last indefinitely.


• Resistors, solid-state capacitors, and other discrete components: these have the same indefinite lifespan as integrated circuits, and are generally more tolerant of temperature changes.


• Batteries and electrolytic capacitors: These contain corrosive chemicals that tend to leak on a timescale of decades; lithium-ion batteries additionally tend to destroy themselves if fully discharged. If you're preserving an electronic device in a museum, you're going to need to remove these. When you want to power the device back up, you'll need to install replacements.


• Circuit traces and wires: these tend to slowly corrode from atmospheric moisture. You'll want to store the device in a dry-nitrogen or argon atmosphere.


• Plastic wire insulation: the plasticizer tends to evaporate on a timescale of decades. After a century or so, the insulation will be brittle and may be cracking from shrinkage. You'll want to re-insulate the wires or replace them before powering the device back up.


• Plastic housings: these tend to discolor on a timescale of years to decades. The main cause of this is ultraviolet light, with atmospheric oxygen coming in second. A UV-protected container filled with the dry atmosphere you're using to protect the circuit traces will greatly slow the discoloration, but won't stop it entirely.


• LCD screens: these are vulnerable to excessive heat or cold, and it's likely that UV light will degrade the dyes that give them the ability to display color. The same temperature and UV protection you're using to preserve other parts should be sufficient to protect them as well.


• CRT screens: these depend on a vacuum inside the screen to function. Depending on the quality of manufacture, they may leak to the point of unusability over the course of 500 years or so. You may need to re-establish the vacuum before powering the device back up, which requires specialized equipment.


• Flash/EEPROM memory: the data on these is susceptible to charge leakage on a timescale of decades to centuries. You can reduce the rate of data loss by cooling the device, but the need to avoid freezing the LCD means you can't cool far enough to get a 500-year lifespan. You're going to need to store the data on some more durable medium and re-write it before powering the device back up.


• Hard drives: the lubrication on the bearings tends to stiffen up on a timescale of years. You'll need to clean and re-lubricate them before powering the device back up, and you'll need a cleanroom to do it in.

There's no way to preserve an electronic device for 500 years in a way that permits immediate re-powering at any time. A museum would, however, be able to preserve one that only requires relatively minor maintenance before using, and the techniques involved are ones that museums commonly employ.