I recently bought a new MacBook Air. There are all sorts of tips about extending the duration of a single charge. Does it matter when I charge it if I want to get the battery's life to be the longest? Should I charge it when the battery is at 50%, 25%, or maybe let it run down to shutdown?
Not sure about when to start charging it, but you should set it to stop charging before it gets to maybe 80% (mine is set to stop at 60%), to prevent the cell voltage getting into the range that causes degradation.
As far as I know the decision about when to start it charging is mostly determined by how much charge you want to have available in the event that you unexpectedly need to use it for a while without mains power. I set mine to start charging at 50% and stop at 60%, but since it is used on AC power it very rarely charges.
Letting it stay near completely empty might be a bad idea, since if you forget about it or are unable to access it for a while, the battery could get into deep discharge, in which case it is bricked as the controller will refuse to charge it ever again for safety reasons, or "safety reasons".
If Li-Ion, you've got x number of charge cycles in the battery's life, before capacity is reduced to 50% of its label rating. Keep it plugged in and charging/charged, whenever you don't need portability.
Maximising number of charge cycles will probably get the optimum use.
Rules of thumb are:
Never leave it flat for an extended period. Ideally don't leave it on charge continuously either.
Modern batteries claim no to have significant memory effect but even so once in a while it does no harm to take the charge down to the last 5% or so. Only crash into the shutdown end stop if you must keep working.
There seems to be a marginal gain in battery lifetime by allowing the battery to cool down before connecting the charger. This applies more to power tools and vacuum cleaners. Laptop current draw isn't anything like as brutal. Cells too hot to touch are too hot to charge well.
I have an app for my phone that seems to indicate the same sort of constrai nts as Tesla advises for their cars. To maximize the life span of the batt ery avoid the bottom 10%-15% of the battery state of charge and the top 10%
-25%. Tesla has a charging setting image with lines at 80% and 90% marked "Trip" implying you should not charge above this level unless you are going on a trip and need the extra range.
My phone app goes so far as to provide charging advice based on battery lif e. It seems show charging between ~25% and 75% results in wear of around 1
4% of a "full" charge. Starting at a lower level than 25% increases the "w ear" a bit but charging beyond the 75% level increases the wear more rapidl y in an increasing scale.
I believe the "wear" is a result of the lithium ions intercalating into the anode and the resulting mechanical expansion. This process slows down at higher charge levels which results in lithium plating onto the anode more r eadily. That's a bad thing. The mechanical expansion issues also play a r ole although I've not seen that described in much detail. I seem to recall a number of 10% expansion at full charge which seems a lot, so my memory m ay not be right. Bill seems to know a lot about batteries. Maybe he will know.
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I saw a video of an Australian gent who showed how to "revive" power tool b attery packs. He was simply using a good battery pack to put some charge o n an exhausted battery pack using two pair of scissors to bridge them. See ms the batteries have nothing that breaks the connection to the terminals. Once the battery had enough charge (~1 minute of "charging") the charger w ould recognize it and finish the job.
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Charging between two states of charge other than a full charge puts much less wear on the battery. A charge from 25% to 75% is around 14% of a full charge according to my phone app.
Heck, I just found out why my phone didn't wake me up this morning... it's out of charge. Starting at 5% the app says charging to 75% will put 17% of a cycle wear on it. So the low end doesn't seem to matter as much as the high end.
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It is a bad idea for the laptop makers to not design in proper battery mana gement. The problem is not so much leaving it plugged in since it doesn't charge once the battery is fully topped off. It's the fact that the batter y is always fully topped off that is bad for it. They should leave the bat tery at 75%-80% most of the time, but then you would need to tell it when y ou plan to use it off battery so it could then top it off before hand. Tha t is really inconvenient for a computer. Works pretty well for a car thoug h.
Tesla still has not factored in that some customers have TOU (Time of Use) utility plans and need to not charge during specific times. They have a ti mer to start charging, but not one to end it. Alternatively, you can sched ule the time when the car will be fully charged and the car will start char ging automatically, but it will start according to the charge level even if it is in the time window of high electrical charges.
Tesla does a lot of good things, but there are a lot of details they have y et to figure out.
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Yes. I have destroyed several laptop batteries that way. But my reason for leaving them on power continuously is that they mostly were being used as a desktop computer and run faster when on mains power.
Keeping the bettery brim full for long periods of time does irreversible damage to the cell chemistry and like all stacks of individual cells the weakest one in the chain is ruined by the others when it is discharged.
It is much worse to leave it with a flat battery for an extended period.
It's often a mistake to let the software guys get involved with battery management. It's less a mistake if the HW mfr does it - they at least have some control over the battery chemistry and vendor source being selected for use and a familiarity with the application load.
Battery mfrs are the most logical people to turn to for this type of information, but in a competative market, they can be cagey about releasing information that is not filtered through a sales network. Unless you're in a position to build or program your own charging system, all you can use this info for is to determine if there's a suitable marriage between the battery and its application.
Letting the end-user program charging and discharging limits and profiles may make everybody feel better, but it won't necessarily produce the longest battery service life.
Don't know about Dell, but the older Panasonic Toughbooks here have circuitry and software support to prevent damage if the machine is plugged into the line all the time. That is, they exp3ct users to do that.
These were not bought new either, too expensive, but made up from various broken, spares examples...
The requirement for specsmanship longevity in various consumer run down tests drives some creative accounting in the battery capacity. You can get a longer runtime by allowing the battery to charge right up to its absolute safe maximum capacity but there are diminishing returns.
The only way to tell is if the thing has no battery capacity remaining when it is not on mains power (like my own Samsung 17" portable now). Hazards of using it for fast computations as a second desktop machine.
It is long enough in the tooth that it isn't worth replacing the battery
- particularly not since Covid prevented any travelling with it. On the move these days I make do with a much smaller lighter 11" unit.
Thanks for the reply. I kept my 5 yr old android on and charging for several months. The battery became swollen so bad the back would no longer close but it still works. Sister got me a new Samsung which is a big improvement. :-)
I don't doubt your claims, but I have had three MacBooks over the last
14 years, and all have been used daily and almost always on the power adapter - yet all have lived for some years and appeared to still have great battery life on the occasions I had to work on battery.