Ask HN: How do you store devices with Lithium-Ion batteries for long-term?

Ask HN: How do you store devices with Lithium-Ion batteries for long-term?
36 points by fouc 2 hours ago | hide | past | favorite | 11 comments

I’m curious about how everyone stores old smartphones and other lithium-ion battery-dependent devices while preserving battery life. Especially when they might want the device to keep working over several years.

I’ve tried charging my backup devices to 50% and storing them in a cool, dry place, but I often forget to do so, resulting in a drained battery by the time I recharge them. I am worried this might be affecting the battery’s longevity.

Does anyone have a better method, such as an automated charging system, for managing this?

I don’t think you want an automated charging system. Maybe make a calendar invite for yourself on the first Saturday of every month to check them. Probably takes at most 10 minutes of your weekend.

Yup, calendar events are the way to go. I recharge certain backup electronics every six months. I’ve probably got 20 different home/life calendar maintenance tasks like that, recurring somewhere between every 3 months and every 2 years.

In a freezer I’ve been storing detachable batteries of a laptop that was mainly used at a desktop. They came out fine after some five years, didn’t do tests before and after though.

It might be helpful to store them in the fridge as opposed to the freezer in some cases. Last time I checked, the highest inflection point in lithium ion degradation with storage seems to be at temperatures at or above 30 C or so [1], so the 5 C typical environment in a fridge would appear to give sufficient margin.

One problem with storing them really cold is that should the device drain the battery, a cold battery can more easily fall under the “minimum cell voltage” threshold due to the changed voltage curve, which can cause laptop batteries to totally fail permanently due to the monitoring chip inside.

Lithium batteries don’t like being charged under 0 degrees Celsius (let them warm up first!), and attempting to do so can lead to the lithium being unable to intercalate into the electrode, causing plating of lithium. The batteries should probably be wrapped in a sealed plastic bag with dessicant in it, to prevent condensation from getting to the internal protection electronics. The device should be allowed to warm up before being removed from the bag to prevent condensation.

[1] https://www.nature.com/articles/srep12967

No idea about anything automated for it but my understanding is that you really can’t prevent the problems. I think I read that 70% is more ideal thoguh, because it will keep a charge longer in the better range for the chemistry. The real problem is that the chemistry itaelf of the batteries will slowly and irreversibly break down over time whixh is why once it discharges past a certain point it may not be safe ever again to charge the battery without reprocessing the materials into a new battery. The safest way is really to remove the battery entirely and replace it once you’re wanting to use it again. This might also make it easier to keep the battery at a safe charge level if you can find something else to handle it.

The types of batteries used in this type of equipment tend to be less robust and more prone to this type of problem than other common equipment with lithium cells in them.

Cells/packs used in these hobby applications typically lack an outer protective shell, and are of the pouch cell type. This makes them more susceptible to damage, but is done for primarily weight considerations likely. Typical notebook or phone batteries will be encased in some form of structure that protects them, and for smaller batteries, like in phones, can prevent the fire from exiting the enclosure to some extent.

Furthermore, these cells/packs are designed for shockingly high instantaneous discharge rates, which means that any accidental release in energy will be correspondingly fast and violent. It seems that protection of the battery is the charger/device’s responsibility, so it’s also easy to accidentally use batteries which have been overtemped/overdischarged/underdischarged/overcharged. (they also have much lower design cycle counts than typical electronics batteries). Typical electronics batteries have a chip in them that will disconnect the battery, sometimes permanently, should any of these conditions occur at some point in the battery’s lifespan.

I would personally recommend against the storage or charging of such batteries indoors without measures to contain any potential fire. For what it’s worth, discharging (and maintaining) the batteries at a low state of charge will also decrease the amount of energy available for combustion.