Tag Archives: smart battery

Exploring Smart Battery Pack Data

Enthusiasts with a variety of interests, ranging from flashlights to electric vehicles, repurpose rechargeable lithium ion cells from laptop battery packs to power their projects. In order to assess the age and health of the cells, people use a succession of tests, ranging from quick tests of initial cell voltage, voltage ~12-24 hours after charging, and discharge tests on analyzing chargers. I looked at the initial cell voltage measurement in the context of information about pack age and history that hasn’t been available to most hobbyists.

To obtain this information, I used PackProbe. The PackProbe project allows quick access to the information contained in each pack’s “smart battery system,” using inexpensive, widely available hardware. PackProbe is part of a larger effort to improve the tools and information available to people re-using lithium ion cells.

 Materials and Methods

PackProbe was used to extract data from a lot of 34 used Lenovo ThinkPad 9-cell 84Wh battery packs (IBM-42T4619) obtained from a seller on the Budget Light Forums. I don’t know more about the provenance of these packs, other than that they apparently came from a single source in a few different shipments starting sometime this summer and totaling hundreds of packs.

Observations and Commentary


  • Most of the packs were manufactured on the 22nd and 23rd of October, 2009. Two on the 27th October, and three on the 8th of September.
  • The packs all report :
    • Manufactuer: SANYO06
    • Chemistry: LION
    • Design Capacity: 84.24 Wh
    • Design Voltage: 10.800 V
    • Charging Voltage: 12.600
    • Charging Current: 5000 mA

Cycle Count

The median charge/discharge cycle count is ~88, distributed as shown:


Initial Cell Voltage

We used the self-reported pack voltage from each pack to estimate initial voltage of each cell. Some of the packs had their PCBs damaged in shipment, which made it difficult to get data out of them, but by applying ~6v to the pack, I was able to read out data. The reported voltages for the damaged packs were quite low, and from my investigation, it appears that they only report the series voltage for two of the banks of cells. If I take this into consideration, and look at the average cell voltage for all the packs, I see the following distribution:


I suspect that all these packs were last charged at about the same time, likely just before their previous users gave up the machines in a round of upgrades (or layoffs). The variation in the voltages could be due to a number of factors, including variations in cell quality, pack wear, charger accuracy, storage conditions, and date of last charge.

Cell Voltage as a Proxy for Cell Wear

Exploring the idea the variations may be the result of pack wear, I’ve tried plotting cell voltage against the number of charge/discharge cycles for each pack:


I don’t see an obvious relationship here. It seems like differences in self-discharge rate due to cell wear don’t explain the variations in voltages within the packs sampled, which all have cycle counts within the normal service life. It may be more useful for packs with large numbers of cycles (>300).

Smart Battery Capacity Measurement

SmartBattery packs maintain an estimate of pack capacity based on run-time data in order to account for aging of the pack. I wondered if initial cell voltage had a relationship to relationship to the pack management circuitry’s estimate of the packs remaining full-charge capacity:


Again, I see no obvious relationship, perhaps not surprising, giving the broad distribution in the reported Full Charge Capacity (in Wh*10):


Further, the reported full charge capacity doesn’t seem to have a strong relationship to cycle count:


It is hard to know what to make of this, other than that there isn’t a clear relationship, which isn’t surprising, given that these packs haven’t been used for some time, and likely require a full charge/discharge/charge cycle before the full charge capacity estimates are accurate.

Discharge Test

I’ve only torn down one of these packs so far and tested the cells. Based on the tests, the full pack would have a capacity of 65 Wh, or 77% of the original capacity (at a relatively high 1C discharge rate). That’s not bad for less than $2.50, but its a pretty severe drop-off over the 103 cycles reported by the pack. It could be worse though, the reported full charge capacity was much lower, just 50Wh, or 60% of the original capacity.


This feels a little too much like writing up a lab report for a not-too-successful organic chemistry lab experiment back in college, lots of  trying to explain inconclusive observations. Even so, I think this work has important implications.

Foremost, the results are a strong indication that initial cell voltage from used packs is not a good indicator of cell wear for used packs, at least with packs of the age and cycle count distribution of our sample.

Second, it should be clear that PackProbe provides useful information for assessing the value of a pack without necessitating tearing the pack apart.

Future Work

I intend to do more work to improve PackProbe and use it to better characterize used and aged lithium ion batteries. I hope others will join in the effort. Opportunities for community contribution include:

Join the Power Cartel forum to contribute and stay abreast of PackProbe development.

The humble Smart Battery reveals its secrets

It took me a little longer than I’d hoped, but I’m able to get most of the information I want out of most of the laptop batteries I’ve tested.

ASUS AL32-1005

Manufacturer Name: AS085NJ35E
Device Name: 1005-28
Chemistry LGC0
Design Capacity (mAh): 5400
Design Voltage: 11250
Manufacture Date (Y-M-D): 2009-6-21
Serial Number: 937
Specification Info: 49
Cycle Count: 254
Voltage: 10.28
Full Charge Capacity (mAh): 1680
Remaining Capacity (mAh): 0
Relative Charge PCT: 0
Absolute Charge: 0
Minutes remaining for full charge: -1
Cell 1 Voltage: 2642
Cell 2 Voltage: 3820
Cell 3 Voltage: 3817
Cell 4 Voltage: 0
State of Health: 0
Charging Current: 0
Charging Voltage: 0
Temp: 20.25
Current (mA): 0

You’ll see that this pack is 5 years old, and has had 254 cycles, which probably puts it near the end of its useful life. Looking at the individual cell voltages (actually banks of parallel cells), you’ll see that that one of them is quite a bit lower than the others, suggesting those cells are closer to failing.
I’m still having trouble with the Dell packs I’ve tested. I can get most of the information I want from them, but they don’t report the capacity of the individual cells properly. The individual cell data isn’t part of the official smart battery standard, but it seems pretty standardized. It may be the Dell packs don’t report that information at all, or it may be that they use a different set of commands to reveal it.

Dell 9T48V

Dell 9T48V
Manufacturer Name: SMP-SDI2.8
Device Name: DELL YXVK234J
Chemistry LION
Design Capacity (mAh): 8400
Design Voltage: 11100
Manufacture Date (Y-M-D): 2013-4-19
Serial Number: 181
Specification Info: 49
Cycle Count: 44
Voltage: 10.03
Full Charge Capacity (mAh): 8428
Remaining Capacity (mAh): 0
Relative Charge PCT: 0
Absolute Charge: 0
Minutes remaining for full charge: -1
Cell 1 Voltage: -1
Cell 2 Voltage: -1
Cell 3 Voltage: -1
Cell 4 Voltage: -1
State of Health: -1
Charging Current: 4214
Charging Voltage: 12900
Temp: 23.25
Current (mA): 0

HP Packs have been a mixed bag. I’ve been able to get a full compliment of data out of some of them, and none at all out of others. I’ll work on fixing it after the initial release.

The code runs on an arduino Yun now, and should be easily adapted to any arduino compatible. I’m going to write a little documentation and release it while I continue to work on it.  If you are interested in getting early access, leave a comment here.

Smart Battery Hacking Progress!

I finally made some progress on reading out data using the “smart battery” interface on laptop battery packs. I’ve succeeded in pulling a number of useful numerical values from three different MacBook Pro batteries from two different manufacturers and one Acer battery pack. I have, so far, failed to get anything out of a different model of Acer pack, an ASUS pack, and an HP pack, but I have some ideas about what to try next. I also have to do more work to make sense of a few of the values I’m getting, and figure out how to read out string data, and figure out if I can get at voltages for individual parallel banks of cells.

In the meantime, here is what I got out of an old Mac battery:

Design Capacity (mAh): 5800
Design Voltage: 10800
Manufacture Date: 15400
Cycle Count: 531
Voltage: 12.23
Full Charge Capacity (mAh): 3073
Remaining Capacity (mAh): 2812
Relative Charge PCT: 92
Absolute Charge: 48
Temp: 31.85
Current (mA): 0
Minutes remaining for full charge: -1

Acer AS11B5E (4INR 18/65-2) 14.8v 6000 mAh 84wH Battery Pack Teardown

I’ve been trying to get my hands on some higher capacity cells than the 2,600 mAh Samsung cells I’ve accumulated so many of, so I’ve been looking through ebay listings for reasonably priced new  battery packs and then checking the photos, descriptions, and even the web for specs and other information that will help me figure out whats inside.

I recently ordered a Acer AS11B5E (4INR 18/65-2) battery pack fro $21.99 with free shipping from In And Out Electronics. They shipped it out quickly and I received it today.


As you can see, its not like most packs made with 18650 cells. Rather than a tough case with connectors and latches for easy installation and removal, this pack has a thin flexible case ribbon cable with a connector. Its clearly meant to be an internal battery that isn’t swapped, but replaced when it wears out. This has been Apple’s approach for about 6 years now, but Acer is using standard 18650 cells, while apple is using custom sized pouch cells.

Apparently the laptop this was designed to power was an absolutely huge media laptop with a 18.5″ display. Crazy!


This pack was incredibly easy to open! .Getting the batteries out of most packs is like shelling a crab, or getting the meat out of a ripe coconut, this was like shelling shrimp, or a soft-shell crab. I just had to pull off strips of tape to get to the sweet sweet battery meat inside.


Look at those juicy cells!  Those are Panasonic NCR18650A cells with a nominal 3,100 mAh capacity! Even better than I expected, and I’ve got 8 of them!

I was hoping for 2,800 or 2,900 mAh cells, based on the specs for the pack that I was able to find which rated it at 14.8v and 84Wh, so the extra nominal capacity was a nice surprise. I’m not sure the source of the discrepancy though. It could simply be that Acer derates the cells slightly.

Another explanation is that these cells tolerate discharges down to 2.5v (most cells should only be discharged down to ~3v) but the capacity between 3v and 2.5v is less than 10% of the total. From the specs for Panasonic NCR18650A cells, it looks like the capacity is ~2,950 mAh if you only discharge to 3v. Avoiding maximum discharge also increases the useful life of the cell.

In any case, in retrospect, some of the clues were there before I opened the pack.


  • 4INR18/65-2: A series of four cells 18mm in diameter and 65mm long (aka 18650), with two cells in parallel.
  • 14.8v: 4 cells in a series works out to a nominal cell voltage of 3.7v (panasonic actually lists 3.6 as the nominal cell voltage for these batteries, but I think thats because of the discharge profile that reaches lower voltage than typical for cells of this chemistry).
  • Panasonic P/N : NCR-B819: This suggests that the pack is manufactured by Panasonic, and so not a surprise that it includes panasonic cells.

Once I had the pack apart, I checked the voltage and found that it only measured 7.8 volts or so, or a bit under 2v for an individual cell. With ordinary lithium ion batteries, that would be a worryingly low voltage. I’m hoping that its less of an issue with these cells. I immediately applied a low charging current (200mA) to bring the pack up to ~3V.


It appears to me that this pack was manufactured in June of 2011, or a bit over 3 years ago. Thats a long time to sit without being recharged, though I’ve had older packs that have discharged less.

I’m keeping the circuitry of the pack intact so I can try to read out information from the battery management board. Once I’ve done that, I’ll put these cells through a few charge/discharge cycles and see how they perform.

Notes: Smart Battery Hacking 2014-08-27

I’m trying to read out information from three different laptop batteries by taking advantage of the smart battery system interface.

The batteries are:

So far, I haven’t had any success in reading out data from any of the batteries, but I have figured out the pinout of the connectors:

MacBook Pro Battery ConnectorIMG_6028

From left to right, inside the wide guide slots on either side:

  • P-
  • Temperature
  • Data (SMBus)
  • Clock (SMBus)
  • Unused
  • P+

 Acer Battery Connector


From left to right, inside the wide guide slots on either side:

  • P-
  • P-
  • Data (SMBus)
  • Clock (SMBus)
  • Temperature
  • Battery Activate / Enable
  • P+
  • P+

The MacBook Pro battery packs make power available all the time, while the acer batteries require a short or low resistance connection between the P- (system ground) and the Battery Activate pin in order to “wake” the battery so it will present voltage, or receive charging current. Furthermore, the Acer packs only wake up briefly if the overall pack voltage is below ~9v or so.

I’m currently using an arduino and using this post as a starting point on how to (try) to talk to a smart battery.