Best practice for charging my cell phone to maximize lifespan?
April 26, 2016 10:32 AM   Subscribe

I recently upgraded my cell to a Galaxy S7 Edge. My previous cell phones had removable batteries, and I preferred keeping a fully-charged backup battery on me or swapping batteries out and charging the batteries separately. The new phone has no removable battery, and I would like to make sure I'm charging the battery in the best manner possible to prolong the life of the phone, but my google-fu is turning up some conflicting information. Please help me figure out an optimal charging method to avoid shortening the battery's lifespan.

I'm generally at a desk Monday through Friday and can easily charge my phone overnight, so I can play around with my charging practices quite a bit. Obviously my actual charging practices will vary a bit, but I'm looking for overall guidelines that I can try to adhere to. I'm already set on using OEM charging accessories only.

I've read the phone's user manual and it's not helpful in terms of which charging/discharging practices will shorten the lifespan of the battery. I understand that the phone's battery is lithium-ion, and what I'm seeing online is pretty consistent in that I won't have trouble with "battery memory" that plagued NiMH batteries. Online advice also seems to agree that heat is bad for the battery's lifespan. Beyond that, the recommendations I've found are inconsistent:

- Keep the battery at or above 50% as much as possible
- Charge when the battery gets to around 40% and unplug the charger at around 80%
- Charge when the battery gets to around 20% and unplug the charger at around 90%
- Avoid taking the battery down to 0% and charging up to 100% on a regular basis
- Drain the battery to 0% and recharge to 100% about once a month
- Trickle-charging is bad for the battery, so unplug the phone from the charger as soon as the battery hits 100%
- The battery technology is better nowadays and you won't shorten the lifespan by trickle-charging - leave it plugged in at 100% battery level
- The battery has 500-1500 rated cycles in its lifetime, but the actual number of cycles that occur before the battery degrades will fluctuate depending on charging practices

Can you help me parse through the useful and non-useful information? What overall guidelines should I try to adhere to?
posted by hootenatty to Technology (9 answers total) 1 user marked this as a favorite
i think just do what you can to minimize total cycles. So keep plugged in when reasonably possible at home or at work.
posted by mercredi at 10:37 AM on April 26, 2016

General LiPo or Li-ion battery practices are the same for cell phones, computers, and all kinds of devices.

In short, don't worry about it too much because batteries are pretty good these days. Charge as often as you can (the smaller the cycle relative to the battery capacity, the longer the battery will last) and don't worry about leaving it plugged in (your phone is smart enough to stop charging when the battery is full, you aren't trickle charging just because your phone is plugged in). If you plan to store a battery without using it for months at elevated temperatures, then leaving it at 100% charge is a bad idea, but in normal use there is no reason not to charge to 100%. Draining the battery shortens the lifespan, so don't do that if you can avoid it.
posted by ssg at 10:49 AM on April 26, 2016 [3 favorites]

Nothing much you can do will really affect the battery lifespan, which is why you see so many differing recommendations. Any of them will work fine because none of them have much effect.

Get a wireless charging doohickey for your desk at the office. It lets you keep the phone topped up without even thinking about it. Samsung has one that offers fast charging.

You might look into apps like Greenify to make the phone use less power so you need to charge it less often, but if you're on Marshmallow the built-in Doze feature should be doing pretty well at that to begin with.
posted by kindall at 10:49 AM on April 26, 2016

ssg's advice is good. Pay attention to that table in the middle of the page.

If you discharge from 100% to 0% you get 300-500 charge/discharge cycles. If you discharge from 100% to 50% you get 1,200–1,500 charge/discharge cycles.

Avoiding deep discharge is very very helpful in lengthening the battery's life. I keep my phone plugged in as much as possible.
posted by gregr at 11:31 AM on April 26, 2016 [1 favorite]

ssg's advice is good. I want to especially emphasize this part: "the smaller the cycle relative to the battery capacity, the longer the battery will last" - i.e., keep the charge as far away from zero as much as possible. Also agree that pretty much every device with a Li-ion battery has a charge controller smart enough to turn off the power when it's full.

The advice about taking it from 100% all the way down to 0% every once in a while is more about recalibrating your battery meter. Designing a useful battery is somewhat at odds with accurately measuring the charge level of that battery; ideally you want the discharge curve to be almost flat, i.e., providing the same voltage at all states of charge, but the way battery meters work is to estimate the charge level based on the difference in voltage (or current) produced as it discharges. If you keep your battery mostly-to-fully charged in order to prolong its life, the voltage level will always be sort of same-ish and it's hard to keep the meter accurate under those conditions. Running it through the entire discharge curve helps put the meter back on track.
posted by Joey Buttafoucault at 11:43 AM on April 26, 2016

If you discharge from 100% to 0% you get 300-500 charge/discharge cycles. If you discharge from 100% to 50% you get 1,200–1,500 charge/discharge cycles.

If I'm interpreting that table (Table 2) correctly, the "discharge cycle" means one discharge to the depth of discharge (DoD) followed by a recharge to full. If so, the discharge cycles would need to be corrected for the more frequent charging to find out what you really want to know - the battery lifetime in terms of actual battery use.

In other words, if a phone takes 1,200–1,500 charge/discharge cycles at a DoD of 50% (i.e. charging to full every time the phone reaches 50%) before its capacity falls to 70%, that would be an equivalent "lifetime" as 600-750 charge cycles at a DoD of 100%. If you adjust the discharge cycles in Table 2 to reflect that, you would get these "full discharge cycle" equivalents:

100%: 300-500
50%: 600-750
25%: 500-625
10%: 375-470

So if my interpretation and math are correct (and please do correct me if I'm missing something!) this information implies that the best charging strategy (to maximize the amount of battery use before the battery starts to lose capacity) would actually be charging when the phone is around 25-50%, not "as often as possible". In practice they're pretty much the same thing, though - you'd probably be charging it every night or something similarly convenient.
posted by randomnity at 2:46 PM on April 26, 2016

There are two opposing battery characteristics. For longest life you would only charge to about 70% and keep it there with a trickle charger. On the other hand, as soon as you unplug it at 70% then you begin using up discharge cycles. Since you cannot control the charger and cause it to trickle charge automatically at 70%, the second best strategy is to always keep it at 100% and plugged into the charger so that you run off the AC and never discharge except when it is in your pocket. This uses the fewest discharge cycles.

So I would recommend always keeping it plugged into a charger when it isn't in your pocket -- sitting on your desk at work on the table at home or in your car. It's easy to just use a USB port on your PC or in your car since you don't need a fast charge if you are always near 100%.

Also to prolong battery life, keep wifi, bluetooth and especially GPS off when you don't need them and aren't plugged into a charger. When using the GPS, the phone can get pretty warm which shortens battery life. When plugged into a charger, it doesn't consume battery life to use the high current services.
posted by JackFlash at 6:04 PM on April 26, 2016

the way battery meters work is to estimate the charge level based on the difference in voltage (or current) produced as it discharges.

As you point out, the Li battery discharge curve is relatively flat which means that voltage is useless for determining state of charge except at the extremes of charge and discharge. So instead, a coulomb counter is used that counts the number of electrons going into and out of the battery.
posted by JackFlash at 6:11 PM on April 26, 2016

Thanks for the helpful responses guys. ssg, that source in particular is super helpful.
posted by hootenatty at 10:08 AM on April 27, 2016

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