# Is battery-charge-stop-at-XX-percent circuitry not cheap? [closed]

I'm curious why IBM/Lenovo ThinkPad line is basically the only manufacturer/brand of mobility devices that includes circuitry and software that allows one to vastly prolong battery life of laptops used as stationary workstations by making sure to never charge the battery prior to it being discharged to below 96%, and having options to start charging only when the battery goes, say, below 46%, and stop charging at, say, 50% or 80%, vastly improving long-term battery health (compared to when the battery is always kept at 100%, and always topped up to 100% all the time, for months at a time, and somehow never happens to reach its advertised cycle count).

Why the other laptops and mobile phones never seem to have any such functionality? Is the circuitry behind such feature somehow intrinsically expensive and not worth it? (Or is it just the case that stationary usage is not accounted for in the design of such other devices?)

• I think the real question is whether or not that 96%/46%...etc options are useful. When the battery reaches 100% it will just trickle charge, which I've read can give software a better idea of the current life of the battery. The rated cycle counts are based on full charge/discharge cycles. Waiting until 96% to stop or 100% to stop will only decrease the actual energy capacity of the battery you're using. – Jarrod Christman Sep 6 '15 at 22:02
• @JarrodChristman, well, if you disagree with 50%, we have another problem. I don't think anyone actually disagrees in regards to 50% -- I recall even Apple's own documentation used to mention that if left unused, Li-Ion batteries are best be charged at 50%. Trickle charging of Li-Ion is not good at all (compared to Lead-Acid, where it is very much so preferred). – cnst Sep 6 '15 at 22:07
• I'm leaning towards voting to close this as too broad, but I'm going to wait for additional community votes or corrective action. It's too broad because the question goes beyond technical factors and involves user experience and expected device usage. Likewise, the meta commentary that I have deleted is a red flag that the question is poorly formed and needs to be closed so it can be edited into better shape. – user16 Sep 7 '15 at 18:07
• @Jarrod Christman: FYI only. LiIOn MUST NEVER be ytrickle charged. Doing so will initially damage and then destroy them. What is done is voltage is held at Vmax and current decreases under batterey chemistry control to some defined %age of Imax and is then terminated. Lower termination = more capacity and lower cycle life. Tghis is very well known by manufacturers. See "battery university" links in my answer. – Russell McMahon Sep 10 '15 at 0:05
• @cnst, Have you abandon this post? If so I would like to edit the post and attempt to reopen the post. – Mahendra Gunawardena Oct 25 '15 at 20:43

IBM/Lenovo ThinkPad line is basically the only manufacturer/brand of mobility devices that includes circuitry and software that allows one to vastly prolong battery life of laptops used as stationary workstations by making sure to never charge the battery prior to it being discharged to below 96%, and having options to start charging only when the battery goes, say, below 46%, and stop charging at, say, 50% or 80%, vastly improving long-term battery health.

Why is this apparently useful feature very uncommon? - Is the circuitry behind such feature somehow intrinsically expensive and not worth it? (Or is it just the case that stationary usage is not accounted for in the design of such other devices?)

There is no technical problem with doing this, and there are advantages in allowing partial state of charge, although not necessarily always as great as you may imagine. There are a number of factors that affect battery cycle life and manufacturers could choose other ones than you suggest.

$V_{min}$ is already controlled by the control circuitry to a level that manufacturers consider safe and this probably varies somewhat between manufacturers. About 3V/cell is usual.

I do not know if patents cover any related aspects but this seems unlikely to have a blanket effect as partial charging in general has general prior art and LiIon technology is now old enough that early patents will have expired.

A major gain can be obtained by simply limiting $V_{max}$ from the usual 4.2V to 4.1V or 4.0V, with a significant gain in cycle life and loss in capacity per cycle.

A significant gain in cycle life can be had by increasing the current at which charging terminates. Usually LiIon / LiPo charge at 1C (mA = mAh) until Vmax is reached then hold voltage at $V_{max}$ and allow $I_{charge}$ to decrease under control of the battery chemistry. If $I_{charge}$ is allowed to decrease to about C/10 = 10% of max rate then the battery attains full capacity but the cell is pushed very near to its upper limit (close to the point where metallic Lithium may "plate out") and the cycle life is decreased. By stopping charge at C/4 or even C/2 capacity is somewhat reduced but cycle life is increased.

Users can achieve their own improvements in cycle life in everyday use at the expense of available capacity. When charging from "empty" at C/1 a LiIon battery will charge at CC (constant current) until $V_{max}$ is reached - usually at around 70% + of full capacity. If charging is terminated at this point (nop CV "tail) then cycle life is increased significantly - maybe 2x to 3x. If charging from empty at C/1 this point is reached at about 0.7 hours = 42 minutes. So a say 40- minute charge from empty about reaches this point.

Generally reducing battery capacity per charge gives diminishing returns. eg if you use half capacity per charge cycle life would need to at least double before you got the same whole-of-lifetime capacity. ie N x 100% = 2N x 50%. In practice you may get say 3N cycles for C/2 capacity so a 50% plus gain in gross capacity over lifetime. Reducing charge to 1/3 capacity may give 6 x as many cycles.
But reducing charge to say 10% of capacity may give not too much more than 30 x as many cycles so still a not much more than 3x gain, if that.
Those figures are 'out of my head' but I believe they are in of the generally correct order and will be enough affected by other factors that they can only be a guide.

Lithium Ion batteries that must have extremely long cycle lives may be charged to about 2.8V/cell. This greatly reduces cell capacity (maybe to 30% of normal max) but allows maybe 8000 cycles. The Mars Opportunity Rover battery is run at this sort of level plus "all the magic they can work" to achieve this sort of result.

References:

Look at www.batteryuniversity.com for more related information.
These pages are relevant:

BU-409: Charging Lithium-ion
"Find out how to prolong battery life by using correct charge methods."

BU-808: How to Prolong Lithium-based Batteries
"Discover what causes Li-ion to age and what the battery user can do to prolong its life"

• This is an interesting answer, and it's also interesting that it starts off giving an impression that charging until full is ok, yet has an interesting conclusion that partial charging is indeed the best sort of deal if you need long-term performance. :-) I don't fully understand it, and LiIon it is hard to read, but I'll +1 anyways. ^_^ – cnst Sep 7 '15 at 17:16
• @cnst Sorry if t's not as clear as it could be. Charging until the CV mode current drops to say 25% of I max is "OK" if yuou want max capacity and don't care as much about cycle life. If you charge only until CV mode I is say 50% of Imax the cell will give more whole of ;liofe capacity but capacity per cycle will be lower. "Road Warriors" who want every last mAh thy can get per cell may think this is not OK. Somebody who wants lower overall cost may think it IS OK. So the measure of OKness varies with user desires. – Russell McMahon Sep 8 '15 at 11:17

All laptops (and especially cell phones) do "fuel gauge" of the battery. All these mobile devices have a battery charger, which can be started or stopped on command. I don't see why that would be a fundamentally expensive feature. Some of them have software that allows user fine-grained control, and others use only on the functionality built into the OS.

“Vastly prolong battery life” is a subjective statement. A little bit internet research reveals (Laptops with the Longest Battery Life) that a new IBM/Lenovo Thinkpad has an estimated battery life of 15+ hours while a new Toshiba Protégé has 15- hours of battery life. Based on the above link it is safe to assume that IBM/Lenovo Thinkpad have a superior battery management technology. If you dig deep into the feature function sets of these laptops you will find that each manufacturer offers a different value proposition. Manufacturers engineer devices in line with the value propositions. There could many reasons behind other vendors not offering the same feature.

Another factor could be intellectual property implications. With the growth in mobile devices, power management and battery technology vendors patent innovations to achieve differentiation from their competition. Therefore investigating recent patent applications and filings is another avenue to explore if IBM/Lenovo or any of IBM/Lenovo business partners have patents that allow them a strategic advantage of the competition. There a few reference that might assist in the investigation process.

From a battery power management technology aspect the cost of power management devices are extremely inexpensive. A quick price check of BQ240X battery charging IC from TI is listed at \$0.85/1ku. There are other great power management IC vendors such as microchip and Fairchild to name a few. It is safe to assume that price might not be a compiling factor.

Most obviously the fuel gauges the most common battery power management software option used by majority of the mobile device users. Looking deeper into a laptop you will find many advance battery management options. Below are the options that are available on my laptop. The reality is that consumers hardly use these option. Therefore, it is difficult to justify investing in engineering a feature function set that consumers don’t typically use, unless there is research to state otherwise. This should essentially answer the second part of the question.

On the contrary there are few enterprise mobile application where the battery charging feature function set are implemented as discussed in the question. So to answer your question, such feature function sets are engineered into devices that meet specific value propositions. Below is device that have the feature function set that are referenced in the question. The battery charger shut off when the battery is fully charged. Similarly the mobile device managers the battery charger per the specification. Both the battery charger, mobile device and battery has smarts to manage the charging.

Vendors encounter many non-technical maneuvers such as intellectual property, business contracts, partnerships, regulations many other in implement battery technologies. It is highly like the reason is non-technical.

Lastly it is worthwhile investigating different type of battery chemistry. Lithium Ion (LiIon) is the most popular and widely used in mobile devices, but Lithium Polymer (LiPo) is fast gaining recognition as a viable alternative. Battery vendors differentiate themselves by offering different value propositions to address battery life.

Below are some links to help get started with further research

References:

• This answer boils down to "I don't know, it might be patents." If you don't know the answer to a question, it's really better to not answer at all. – 410 gone Sep 7 '15 at 6:32
• @EnergyNumbers ...OR you could summarise it as "there are no good technical reasons". – Russell McMahon Sep 7 '15 at 9:43
• Yeah, this is kind of an empty answer. The heading, comparing the initial capacity of two brands of laptops, is especially off. If you'd link to a test where both were used stationary for a period of a year, and manufacturers recommendations for such use were followed, through software, not through physically disconnecting the battery, then the resulting run-time was measured, I wouldn't be surprised if the Li-Ion battery that was trickle-charged wouldn't even have enough capacity on the lower end to let the laptop shutdown safely when the power does reach towards the end. – cnst Sep 7 '15 at 17:22
• @cnst I was not meaning to criticise this answer - just offering a counterpoint to EN's comments. The answer does not address your main point well but has some good information in it. Your main question is ~= "Why do not more manufacturers provide a mode that cycles the battery in the ~= say 3.4V - 4.0V range per cell when used in "desktop" mode? THe battery university site that Mahendra cites provides more on the subject. – Russell McMahon Sep 8 '15 at 11:46
• @Mahendra - Not meaning to be rude, but I think you have not fully understood his main point. This question is not re operating for maximum runtime on a single charge but rather re operating the battery WHEN MAINS CONNECTED in such a way that battery cycle and calendar lifetime is optimised. He susggest that this may be achieved by holding battery voltage well away freom eithr Vmax of ~= 4.2V and Vmin of 3V when in "gvrid connected mode. He is saying that Lenovo do this but nobody else does and he wonders why. My answer covers a range of areas as well and is not focused solely on his method. – Russell McMahon Sep 9 '15 at 9:18