Any way to stop battery charging at under 100%?

Question

Research has shown that a battery kept at 40% charge will retain 96% of capacity after 1 year (at 25 degrees C), while a battery kept at 100% charge will retain only 80% of capacity after the same period of time.
Is there any way to control the maximum charge level, so that the battery stops charging after a certain point (say, 40%, or 75%). Thanks.

Answer 1

Lyssa wrote:
Do you have a link for the article you read that has this info? I'd love to read it!
Like the above poster said, you can't control how long the battery charges--unless you unplug the cord yourself.
I would like to mention something for you. My battery is 11 months old, and has maintained 98% of its original capacity. Within the next 4 weeks, it will hit the one-year mark, and I don't anticipate it failing on me before it has reached the typical lifespan of ~300 charge cycles. I wouldn't be surprised if it hangs on for another 100! It currently has 264 to its credit. I think my battery is doing pretty well--and I run off it for a few hours nearly ever day
Of course that's an expected outcome with most lithium rechargeable batteries. However - they do have their drawbacks including an inherent loss of total capacity from the aging process.
The best thing for your battery is to USE it, even if you're sitting at your desk much of the time. Unhook the power charger for 30 minutes, or an hour, then reattach it. If it doesn't seem to be working properly, calibrate it.
It all depends. Using a battery and charging it to near maximum by definition cut capacity because of some loss of the electrolyte solvent when it gets vented. In NiMH batteries, the solvent is water. It's a non-water solvent for lithium rechargeables. If it's not vented, it could potentially explode. Using a battery every day will result in noticeable loss of capacity. There's a balance to overuse and underuse of a lithium rechargeable battery. Apple recommends that a battery be partially drained at least once a month. My MacBook is set up with an iCal reminder to use battery power once a month.
The 40% you mentioned from the article is something I've heard before, but I believe it was mentioned in relation to storing your computer for an extended period of time(ie several weeks). If you wanted your battery to be healthy when you returned, you wanted to store it after you'd partially discharged the battery.
I've brought up the extreme case of first generation hybrid car batteries. They employ a different strategy for charging that takes advantage of an always present charging source (the internal combustion engine and generator). They take advantage of the extreme case where the battery is intentionally kept between 40-65% of charge nearly all of the time. Going a little bit under or over this isn't a big deal. This keeps it from the extremes of near max charge and near min charge; both tend to reduce battery capacity for different reasons. The electrical output is only a supplementary power source used during peak demand periods. I've heard of some original batteries from Toyota Prius taxis that have survived 400K miles of service; that probably meant 100,000-200,000 of the shallow charge-discharge cycles. The fact that only a small range is needed means that they can continue this use for a long time. It probably would have been noticeably degraded after maybe 1000-2000 20-100% deep discharge cycles. The total amount of energy drawn over the lifespan is many times with the small discharges compared to deep discharges. You're typically using 25% of the charge hundreds of thousands of times rather than 80% of the charge a few thousand times.