Try if they charge. If yes, delete whatever data you find on them, then bring them to a recycling center. If no, think for a moment if you are important enough for someone to repair a phone just to get your data from ten years ago. Unless you have high security clearance for the government or a really large company, the answer is probably no. There are easier ways to get more current information about you.

It’s not something I worry about. Electronics recycling centers get so many old devices that I’m sure that mine are just lost in the mix. Even when I drop them off at my city’s recycling yards, they’re sending old electronics off by the shipping container-load. It gets shredded, or otherwise destructively disassembled for materials, not for components.

The possibility that anybody would bother to try to extract the memory from my old phone for forensic recovery of the encrypted data is so remote as to be non-existent. Data recovery companies charge a lot of money for the service, because it takes expensive, specialized equipment. What would somebody hope to get by doing it for random, old phones? I mean, if it’s dick pics they want, plenty of guys would be happy to send them voluntarily.

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If you’re recycling it and not donating it, you can take the battery out and drill through the memory chip.

They can all have the battery removed if you open them up, but it’s very unlikely someone will go through the effort to try to find anything useful on an old device.

I would just destroy the touch screen.
Without it, you can’t unlock the phone or give a PC permission for data access or USB debugging.
The danger of someone disassembling the phone to mount its flash storage in another device is negligible.

My only concern is if there’s an ssh key on there. If you’re clever ahead of time, every phone has a new ssh key that can be trivially disabled on the far end.

If you’re tech savvy, buy a charger, see if the phone works, copy your data from your phone or computer, and try to do a DoD wipe on your phone. If you can’t find any instructions on how to do that on Google, then just try a normal factory reset, sign into a dummy Apple/Google account (with no personal information), then fill up all of the storage with some junk files before recycling. You can repeat this a few times if you really want to.

If it doesn’t work after charging, I’m not sure you can do anything without disassembling the phone. If you manage to do that, take out the battery, store the battery away from heat, and then see if you can find the storage chip (might be called NAND flash; it shouldn’t be anything that says DRAM or RAM). Destroy that chip by drilling a hole through it or cutting it off, then recycle everything else.

If they are iPhones I would be less worried about the data, Apple has had a good track record of using encryption of the device.

If you want to be sure that you get the data removed, look up an ifixit guide for your phones, open them, then take the mainboard out and break it into smaller peices.

You are not interesting enough to do a complicated and difficult board repair.

Easiest would be if you have access to an angle grinder or orher heavy duty cutting tool, and cut the phones into peices.

Destroy it with fire! /s