Notes on battery life, gauge and manufacturers

[dr_st]

Battery life of laptops is a topic of frequent discussion. The general consensus regarding the life expectacny of Li-Ion batteries seems to be that the major factors shortening the life of batteries and reducing their capacity are time, usage, frequent full discharges, and heat.

In the Thinkpad community people often use the battery meter in the Power Manager / Battery Maximizer as the primary source of information on the full charge capacity of the battery. Even though it is not always accurate, it does tend to be as accurate as one can get. Comparing the "full charge" capacity to the "design" capacity lets one know how worn the battery is and how much its battery life has degraded compared to the original.

In the following FC will denote "full charge capacity" and DC "design capacity".

My own personal experience with batteries from the three manufacturers supplying IBM/Lenovo genuine batteries (Panasonic, Sanyo, Sony) showed that the battery meter behaves in distinctly different ways between the three brands, and pretty consistently within the brand (at least as far as my limited experience can tell).

Assuming the battery meter stays accurate, this leads me to draw the conclusion, that battery life over time varies a lot between manufacturer. However, this assumption does not always hold - I've seen cases where the battery meter is plain wrong, regardless of how many times you calibrated.

Here is what I noticed:

Panasonic:
When first used, shows FC=DC, and stays this way for a cycle or two, after which FC degrades roughly linearly in time and cycles during the life of the battery.
Effect of calibration:
On a battery that is frequently partially discharged, the meter is off, and a full discharge can gain or lose up to 5Wh in my experience. The actual capacity is usually somewhere in the middle.
Examples:
2.5 year old 9-cell battery (T60), ~200 cycles. DC=84.24Wh, FC=69.67Wh
1.5 year old 9-cell battery (T60), ~130 cycles. DC=84.24Wh, FC=74.02Wh
2.5 year old 6-cell battery (T60), ~10 cycles. DC=56.16Wh, FC=54.80Wh
Overall, the Panasonic batteries have shown reasonable resistance to the effects of time, and even after a few years can still hold a noticeable percentage of their charge. I once sold a 3-year old X32 whose 6-cell battery held ~40Wh of the original 51.84Wh (~77%).

Sanyo:
When first used, show FC>DC. That's right, as if the battery comes overcharged and holds more than it is designed. Experience shows up to 3Wh difference between FC and DC.
For about 1.5 to 2 years since manufacturing/use date the battery meter still shows FC>=DC, although FC varies within 2-3Wh. The actual usage and the number of cycles seems to have no effect whatsoever. However, after the mentioned time period, battery starts losing capacity like crazy, and FC can often go to under 50% of the DC in a few weeks/months.
Examples:
4 year old 6-cell battery (T42), ~120 cycles. DC=47.52Wh, FC=21.43Wh*
1.25 year old 7-cell battery (T61), ~300 cycles. DC=65.52Wh, FC=65.83Wh
0.5 year old 6-cell battery (T60), ~30 cycles. DC=56.16Wh, FC=56.48Wh
Effect of calibration:
With each partial discharge FC goes down a bit. A full discharge usually "gains" all the charge back. This is during the first phase of the battery's life, while FC>DC. When the battery is old, my experience has shown that the battery gauge is no longer accurate at all. For instance on the battery marked with * above, the gauge refuses to go above 21.43Wh, even though the battery clearly holds more than that (laptop lasts for 20-30 minute working on 0%). On the other hand, I've seen old batteries, where FC was <10Wh, and the actual capacity was even lower, and the meter dropped from 50% to 7% in seconds.

Sony:
With these batteries I have very limited experience, and I have not owned one to determine how it behaves over time. However, one interesting phenomenon that I observed, is that, unlike with the other two manufacturers, charges and discharges seem to have no affect on the battery gauge, at least in the beginning (first few tens of cycles). It always shows FC=DC. I assume that at some point it does start showing wear.

All in all, these phenomena may be caused by differences in the way the manufacturers calibrate the gauge, and not by actual differences in battery chemistry. But it is still interesting.

I am curious to learn of other people's experiences and statistics.

[underclocker]

Very nice write up and start to documenting one of the mysteries of laptops.

I have had similar results with hundreds of T4x batteries. Firstly, I think it should be noted that all IBM T4x batteries are really excellent. They last for hundreds of cycles and several years. We really are splittling hairs a little with this analysis, but inquiring minds do want to know...

My basic impression is that the Panasonic batteries are superior, both their cells and gauge calibration. They just seem to have more capacity over time and are not diminished as much as others by age.

The Sanyo batteries are very good batteries but their gauges are not that accurate. Occasional full rundown and recharges are necessary to keep them properly set. Frequently, three to four cycles of full rundown/recharge will add several Wh to the capacity. But beware, batteries that already seem opimistic with their stats will loose several Wh! It works both ways.

Sony's seem inconsistent to me and I haven't had many. I can not comment much more on those.

One note, I'd say Sanyo's are used in 9 of 10 laptops with the other splitting the remaining 10%.

[jwthinkpad]

Thanks for the writeup.

Unfortunately, the lenovo store and the outlet store don't tell you the maker. http://goo.gl/WfbD

I've looked on ebay and craigslist, where you can just ask the seller what the maker is. Any other good places to look that tells you the maker?

[dr_st]

Lenovo typically posts the part number, which like you say, does not specify the manufacturer. If, by chance, they post the FRU, then it can be compared against the data in the Hardware Maintenance Manual to determine the manufacturer in some cases. But I wouldn't count on it.

In the case of the 8-cell tablet battery, the HMM only lists Sanyo as a manufacturer anyways.

[dr_st]

I decided to make a follow-up of the batteries I have in my possession to see how much their capacities changed over the past 8 months, since I last measured it in May 2009. The 4 T60 batteries are used interchangeably on my two T60s, with any battery being stored in a drawer, at around 50% charge, when not in use. The T42 battery is permanently in the T42, and is typically plugged in.

The data is summarized in the table below.

Code: Select all

Battery	Brand		Manufactured First used Cycles	Design	  01/2010	  Remaining 05/2009	Change/8mo
T60-9c-1	Panasonic	08/2006		10/2006	216		84.24		69.33		  82.30%	69.68		-0.50%
T60-9c-2	Panasonic	05/2007		06/2007	217		84.24		74.31		  88.21%	74.02		+0.39%
T60-6c-1	Panasonic	07/2006		08/2006	 55		56.16		53.61		  95.46%	54.80		-2.17%
T60-6c-2	Sanyo	    07/2008		12/2008	 72		56.16		56.72		 101.00%	56.48		+0.42%
T42-6c-1(*)Sanyo		 03/2005		05/2005	172		47.52		17.38		  36.57%	21.43		-18.90%

First, I would expect that the gauges have a deviation of about 2Wh either way, so actual capacity may not be as accurate, but within these margins.

The exception is T42-6c-1 which I think is completely shot as far as gauge accuracy goes. In the past week since I took the reading the full capacity gauge actually went down to <10Wh, but the battery still feels like it holds 20Wh more or less - it ran for over 20 minutes after reaching 0% on full CPU load.

Interesting observation of the two 9cell Panasonics: T60-9c-1 has been used very sparingly over the past months, and added less than 20 cycles. T60-9c-2 on the other hand has been used as the main battery in my work laptop, and added about 90 cycles in this time frame. Despite the differences in use, the capacities of both batteries stayed on the same level, with no decline at all during the past 8 months.

T60-6c-2 still shows higher capacity than design at some points, which is incredible for a battery 1.5 years old. But according to my guesses above, if the patterns I've noticed in Sanyo batteries are correct, it should start losing capacity pretty fast pretty soon.

It will be interesting to see where they stand in a few months. I will probably be updating every once in a while.

[dr_st]

Here's another update (almost exactly six months since the previous one).

I'm excluding the old Sanyo battery from the T42, cause I couldn't get new data (don't have the laptop at hand). However, I am adding a new contestant - a 4-cell battery from my wife's X61. Unfortunately, I do not have previous measurements to compare to, but it is a good starting point.

Code: Select all

Battery	Brand		Manufactured First used Cycles	Design	  07/2010	  Remaining 01/2010	Change/6mo
T60-9c-1	Panasonic	08/2006		10/2006	220		84.24		71.30		  84.64%	69.33		+2.80%
T60-9c-2	Panasonic	05/2007		06/2007	271		84.24		74.31		  86.17%	72.59		-2.30%
T60-6c-1	Panasonic	07/2006		08/2006	 91		56.16		51.36		  91.45%	53.61		-4.20%
T60-6c-2	Sanyo	    07/2008		12/2008	120		56.16		53.18		  94.69%	56.72		-6.24%
X61-4c-1	Sanyo	    03/2008		12/2008	 99		37.44		28.29		  75.56%	 n/a		  n/a

First, I would expect that the gauges have a deviation of about 2Wh either way, so actual capacity may not be as accurate, but within these margins.

Again the two 9cell Panasonics stay almost constant, fluctuating within the margin of error. Again despite one being used a lot, and the other almost not at all. Almost no change in capacity within the past year and a half.

The 6-cells started losing some capacity, but the Sanyo, despite slightly accelerating downhill, is still nowhere as fast to go down as I would expect. X61-4c-1 is a bit older though, and there you can really see the capacity going down. Percentage-wise it has degraded far more than the Panasonics which are significantly older and have significantly more cycles.

It will be interesting to see if the T60-6c-2 reaches that point by the next measurement point.

Stay tuned for the next update in 2011!

[dr_st]

The bi-yearly battery update is up!

Some new entries in the table this time with the T410 batteries, a new 9-cell for the T42, the X61 8-cell battery (previously not measured) and the T42 old 6-cell which is back.

Code: Select all

Battery		Brand		Manufactured First used Cycles	 Design	  01/2011	  Remaining 07/2010		Change/6mo
T60-9c-1 	Panasonic	08/2006		10/2006		222		84.24		71.47		  84.84%	71.30(220)		+0.2%
T60-9c-2 	Panasonic	05/2007		06/2007		297		84.24		70.98		  84.26%	74.31(271)		-2.2%
T60-6c-1 	Panasonic	07/2006		08/2006		114		56.16		50.68		  90.24%	51.36(91) 		-1.3%
T60-6c-2 	Sanyo	    07/2008		12/2008		167		56.16		46.65		  83.07%	53.18(120)		-12.3%
T42-6c-1 	Sanyo	    03/2005		05/2005		201		56.16		16.20		  34.09%	X					n/a
T42-9c-1 	Sanyo	    04/2010		10/2010		85 		77.76		73.51	  	94.53%	X					n/a
X61-4c-1 	Sanyo	    03/2008		12/2008		100		37.44		28.26		  75.56%	28.29(99)		 -0.1%
X61-8c-1 	Sony 	    08/2008		11/2008		51 		74.88		74.88		  100.00%  X		  		  0.0%
T410-6c-1	LGC	   	07/2010		12/2010		10 		56.16		56.15		  99.98%	X					n/a
T410-9c-1	Panasonic	09/2010		11/2010		4  		93.96		95.74	  	101.89%  X					n/a

As you can see, some batteries were hardly used in the period, others were used extensively. The comparison thus is not 100% fair, but some interesting observations can be made:

Panasonic batteries still hold their charge, some almost 4.5 years after manufacturing date, some with almost 300 cycles - and still over 80% of the design capacity.

The T60 Sanyo battery went the way all Sanyo batteries go - sudden and quick degradation - 12% lost compared to the last measurement, and most of it were in the past 1-2 months (I observed it). So there's another example to the general trend.

With that said, I begin to think that even with how bad Sanyos degrade, their gauges actually make it seem worse than they are - once they reach 0%, they can hold for surprisingly long before the laptop shuts down.

The Sony battery, even after 50 cycles still shows exactly 100% of the design capacity. I think it has more to do with the way they calibrate their gauge than with actual battery status.

Very interesting stuff with the T410. LGC is a new contender, and seems to behave somewhat like the old Panasonics - showing just a bit capacity lost after several cycles. And the Panasonic battery - seems to behave like the old Sanyos - it actually seems to come overcharged, holding more than the design capacity! That's the first Panasonic I've had that behaved this way. I wonder if some battery rebranding took place - will be interesting to see how this battery fares over time.

Finally, something I've noticed about manufacturing dates of batteries. It seems that IBM/Lenovo's stock of spare batteries tends to be older than the units they ship with laptops. From the table above, T60-9c-1, T60-9c-2, T42-6c-1, X61-8c-1 and T410-9c-1 came with the laptops, and show just a couple of months between manufacturing date and first use date. However, T60-6c-2, T42-9c-1, X61-4c-1 and T410-6c-1 were purchased as aftermarket, and were 5-9 months old when first used.

[Brian10161]

Very interesting read, I have a T60 with the Sanyo battery. I'm currently at 240 cycles, 37.22 Wh with a DC of 56.16 Wh. When I got it, it was sitting around 30 Wh, but I did a recalibration on it and it came back up.

I am waiting for a 9 Cell (Unsure of manufacturer). Really interested to see how long it will run the computer.

Again, great post!

[dr_st]

Very interesting read, I have a T60 with the Sanyo battery. I'm currently at 240 cycles, 37.22 Wh with a DC of 56.16 Wh. When I got it, it was sitting around 30 Wh, but I did a recalibration on it and it came back up.

How old is your battery (manufacture date)? I've found that with Sanyos the age has a far bigger effect on remaining capacity than the number of cycles.

[Brian10161]

Here's the information that Power Manager reads:

Date of Manufacture, April 5 2007
Date of first use, May 2007

[dr_st]

Your numbers are what I would expect from a Sanyo of this age, perhaps even better than average.

[Tõnis]

I have only had Sanyo batteries (three of them), and they seem to exhibit the patterns you've noted. Even the oldest one behaves like the one you describe with very little charge left. They all came through showing FC>DC in the beginning and seem to hold it like that for a while. I don't remember exactly, but it seemed like 20 cycles before it dropped below 100%. But the comforting thing about this is that I read elsewhere that this is normal for Li-Ion batteries in general regardless of the maker. Could the fact that these Sanyos exhibit this behavior while the others don't mean that the Sanyos are better? I don't know, but thanks for sharing your interesting findings.

[Brian10161]

My X60s has an 8 cell in it I think, not too sure.

DC = 74.88 Wh
FC = 37.89 Wh

I did a calibration on it, and it came up from 32.33 Wh to 37.89 Wh. I noticed that it stayed at 32.33 Wh until the charge gauge read 5%. It sat at 5% for aproximately 30 minutes, then the FC jumped up and then the gauge continued to drop.

Both my T60 and X60 did this, so maybe another thing to think about when your capacity drops down? I don't use the IBM recondition/re-calibrate method. I just let the computer run until it turns off.

When it hit 4% it went up to 38.79, I let it run until it died and it went up a little further. Now at 38.79 Wh. Not too bad IMO,

[anachronism]

My t42 has a 6-cell Sanyo manufactured in 2005-01, first used 2005-03.
Started with 47.52WH, down to 11.20Wh with 202 cycles.
I get a reported 40 minutes with minimum display, cpu, and wifi running.
However, I recently decided to test that 40 minutes out, and apparently the system can run for 61 minutes until it is forced to shut off.

[dr_st]

Same experience as with my Sanyo. Their gauge accuracy degrades with the age as well, not just the battery.

With that said, I begin to think that even with how bad Sanyos degrade, their gauges actually make it seem worse than they are - once they reach 0%, they can hold for surprisingly long before the laptop shuts down.

[underclocker]

Here's my follow up. I've probably owned 75-100 T60 six cell batteries at this point. I have two dozen in my basement that have failed prematurely.

Without question, Panasonic batteries are the best. They report accurate readings, last a long time and are rarely (if ever) defective.

Sanyo batteries are good, but they degrade rapidly with time whether used or not, and they prematurely go bad with some regularity.

Sony batteries appear to be poor quality with inaccurate guages. 18 of the 24 defective batteries that I have are Sony. Most have well under 100 cycles on them, several had under 40 cycles before they failed. Oftentimes, they will show that they hold the full 56.16Wh capacity, but after two to six complete rundown cycles, they eventually adjust their guages, either failing or showing from 2 to 20Wh. They seem to develop defective cells or connections between the cells since they all show the same type of failure, they drop from 80-100% to about 4% after running for a short while. I have yet to own a Sony battery that has not failed or plummeted below 20Wh with low cycles.

Note: If you have a Sony battery showing unrealistic statistics, try doing 3 to 5 complete rundowns, that will reveal the truth.

The Lenovo "recalls" were a joke, very few that qualified within the limited time windows for qualifying. Six year old T4x batteries are still running stronger than most T60/R60/T61 batteries. The Sony's should be recalled.

I have owned far fewer nine cell batteries, but only one has been defective. The nine cell batteries seem to fare much better than the six cells.

[dr_st]

It's a bit early for my semi-annual update (and the new update will include a couple of new batteries), but in the meanwhile just a testimony to how terrible the Sanyo gauges are.

For the past several months my T60 6-cell Sanyo has been steadily degrading from 46.65 (recorded at last check) to about 36.something. A very rapid decline, but apparently mostly in the accuracy of the gauge. The battery would literally run for half an hour on 0%. After several charge-discharge cycles spanning several weeks - poof, the gauge returns to 46.22.

Edit: January 2017 Update is available