It’s from spring of 2012, which makes it a bit dated in some regards, but I still found it informative, particularly since most of the battery packs I’m getting are of a similar vintage.
Some things I found interesting:
Relative to 18650 cells, prismatic LiIon are ~1.4x more expensive, and pouch packs are 2x more expensive for the same capacity.
At the time, 18650 cells were clearly HPs focus for price/capacity. They were, however, using prismatic cells and pouch-packs for thinner form factors.
Pouch cells are relatively easy to get 1000 charge cycles from because they can expand and contract as needed when being charged and discharged, reducing the pressure that degrades the electrodes. The downside is that cells can also expand due to gas generation, which can damage the pack and/or other components.
At least for the products being discussed, HP seemed to be transitioning from prismatics to pouch packs.
Safety regulations limit companies from stuffing more than 100Wh into a single battery pack. This, combined with improved capacities, have lead to the demise of 12-cell extended runtime packs.
At the time, HP was using LG 3000 mAh cells for their high-capacity 18650 packs.
Apple shouldered the growing-pains of getting pouch-cell pack design and manufacturing right.
Because the cells are a commodity, HP tries to distinguish its packs on quality, reliability and manufacturability. This has led them to use conformal coatings on circuit boards to protect against shorts and corrosion. They’ve also switched from wires to flex circuits within the packs for improved reliability and their pouch-cell packs have moved to welding the cell contacts directly to a PCB.
Their primary suppliers are Panasonic, LG, Samsung.
Among Chinese cell manufacturers, they’ve tried to work with a few, but the economics haven’t worked out. B&K is a qualified supplier for some of their packs, but HP doesn’t ship many of their cells.
I picked this HP TD06 (Series HSTNN-UB85) 11.1V 62Wh battery pack up at RePC for $1 at the same time I got the ASUS AL32-1005 pack I posted about earlier. Based on the nameplate pack voltage, it was one of only a handful that used newer 3.7v lithium ion cells out of the hundred or more packs they had.
It was also the only of TD06 pack using newer cells; there were 3-4 labeled with a 10.8v voltage.
Peeling the label back gave a tiny peak at the cells. I was able to separate the two halves of the pack case with a thin bade, pliers and a bit of elbow grease.
The lavender-wrapped cells are clearly made by Samsung (not a big surprised, given that the pack label indicated that the cells were made in Korea. The remaining marking is ICR18650-28A. These cells are rated for 2800 mAh of charge capacity, which isn’t a surprise given the 62Wh claim. Unfortunately, they must be charged to 4.3V to achieve that capacity. When charged to the more common 4.2V, they have about 7.5% less capacity.
The battery management seems to be divided between two chips with a lot of pins. One is labeled M37512, FC024, J2C5D. The other is 20020 ??05. The first chip appears to be an 8-bit M37512-FC MCU from Renesas intended for…battery pack applications. I’m not sure what the second chip appears to be a RS20020. This is a companion chip for battery pack applications. I can’t find information on what it does, exactly, but it seems to have connections to each cell, and to the MOSFETs that can switch the flow of current to or from the pack on and off.
I picked this ASUS AL32-1005 11.25V 5600mAh 63Wh up at RePC for $1. Based on the nameplate pack voltage, it was one of only a handful that used newer 3.7v lithium ion cells out of the hundred or more packs they had.
Labels for the positive and negative contacts were, helpfully, molded into the plastic.
Removing the plastic sticker exposed part of the cells, but to get them out, I had to rip the plastic case apart, with some pliers and elbow grease. Pack voltage is reasonable, so its unlikely that any of the cells are completely shot, but at the point, I don’t know how much use they’ve suffered. I’m leaving the circuit intact for now so I can try and read out the smart battery information so I can see if there is any correlation between that and the results of testing the individual cells.
The cells themselves look like they are made by LG. They are all labelled LGDC118650. All the onces I can see also have I1245xxxxxx, MED45DxC1, where the ‘x’ represents a position with a number or letter that varies from cell to cell.
From what I can tell, the manufacturer is LG, and they are 3.7V, 2,800mAh cells, which is pretty much what I expected based on the specs printed on the outside. One of the only english-language pages I found mentioning these cells suggested they had a charge termination voltage of 4.35v, but I’ve found nothing else to corroborate that.
The battery management chip is labeled bq 20Z45, 95K, CP7L, which looks like the TI bq20z45, an all-in-one battery management chip.
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