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Comment by radlad | Hacker News Reader

I find it interesting that my 2021 MBP's "health" was down to about 85% after the first year, but has only decreased to 82% after two additional years. I have 653 cycles now.

Assuming that's accurate, and batteries spend a majority of their usable lifetime around this capacity, perhaps battery estimates should be based off of the 80% capacity mark.

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80% SoH is the de-facto industry standard for EoL/replacement. Mostly because after that you will eventually get a "knee-point" in your degradation curve at which operation is risky and largely inefficient.

Without knowing specifics, your MBP might have had issues with an individual cell such that initial capacity dropped significantly until the cell was disconnected.

I've seen several laptops start out in the 90-95% SoH range, drop off quickly to the mid-80s and stay there for a very long time. Similarly for iPhone batteries, they go below 90% pretty fast, then each % off takes longer and longer until they actually start dying. Maybe that's due to different baselines though, BMS of laptop batteries normally refer last-full energy to the design energy, which is probably just a fixed value in an EEPROM and might not ever be reached due to a more conservative charge cutoff and tolerances.

Enough cycles and you get a free pillow so the risk comes with rewards sometimes!

The number is, I believe, simply peak voltage. And personally I find the measure grossly misleading: an iPhone with an 80% battery has an almost useless runtime. It definitely isn’t 80% of the original runtime.

My iPhone could handle about 2 days with heavy usage. It was reduced to a day after 1 year. Now after 2 and half years, the battery dies in about 12 hours with the same usage. The battery health is 83% according to iOS. So it’s definitely not a good indicator for real life usage.

I use https://apphousekitchen.com to only charge to 80%

Apple added a feature that only charges to 80% if you're only using it while plugged in (and discharges to 80% if not disconnected).

That made me uninstall aldente again.

I struggle a bit with this concept. It feels silly to me to only use 80% of my laptop's battery capacity in order to... avoid my usage bringing my battery's capacity down to 80%.

OK, so it can go below 80%, but if it takes 3-4+ years, I'm not sure I care. (Don't get me wrong - I do of course use the built-in intelligent charging on Apple and Android devices. No reason to charge a battery to 100% when I'm going to plug it in for bedtime in a few hours anyway.)

It might make sense if you occasionally use the full 100%. But for most people I expect it makes more sense to just use 100% of the capacity and then replace the battery if/when it degrades. For some reason, many people seem to have an aversion to replacing the battery in phones. Yes, it's expensive, but those same people will often replace the entire phone which is much more expensive!

For most people they are not using 100% of capacity every day. In fact large numbers of laptops are primarily used plugged in and just move from desk to desk. In that scenario charging to 80% has no downside. The upside is that your battery may last longer. If you are keeping your laptop for longer than 2-3 years that might be worthwhile.

It's more than just going down to 80%. After a while the battery will essentially fail entirely and not hold a charge, or swell up and push around other components of the computer, and it becomes a fire hazard.

I have an M1 MBP and I use it 95% of the time at my desk. I use Al Dente, and if I'm going to be using it away from my desk or I'm going on a trip, I'll just click the button to fully charge it. Even if I forget, the battery life is good enough that 80% is usually enough.

The idea of not charging all the way is to get more total use out of the battery.

These batteries degrade with use. They degrade faster when they have a high charge or a low charge. Suppose each day you used 50% and charged at night. That's a cycle every two days.

If you are doing that by going from 100% to 50% and then charging back to 100% you will get some number of cycles before you need to replace the battery. Let's say it is 1000. You'd need to replace the battery after 2000 days.

If instead you do your 50% per day by going from 80% to 30% and then charging back to 80% you are operating in a charge range that has a lower degradation rate, so now you might get 1500 cycles, or 3000 days.

I understand it increases the total lifetime of the battery, and certainly I do know a few people who are still using their iPhone 8, but most people seem to replace devices every 4 years at least. I just don't find the tradeoff worth it, but I understand from some of the sibling comments that this is probably most useful for people who don't typically run on battery power.

I was pretty careful with my 4.4yr old Intel MBP, nearly always using Charge Limiter to max at 80% or so.

It's at 500 cycles now, the battery has been declaring it recommends service for a year, and taking it out to cafes limits my work time to maybe 3 hours max (starting at 80%).

There were at least one or two occasions where it 'cooked' itself to death inside my backpack though, when it didn't sleep on lid close as expected.

Not sure how big an impact charge limiting has made (is my battery life better? did I avoid pillowing?). Or the self-cooking. But that has been the life of this computer.

600 cycles in 4 years is pretty high IMO. Do you carry it around all the time without it being plugged into socket ?

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