Canon BP-511A

What's in BP-511 batteries?

https://www.camerahacker.com/Canon_Accessory/BP511_Disassembly.shtml

https://www.camerahacker.com/Forums/DisplayComments.php?file=Digital Camera/Canon/DR-400_pinout.html

From that quick search, it's not clear what exactly is on the little BMS board.

Top: two new batteries bought 2024. Bottom: original batteries bought 2005-2008.

Teardown

front + flipped back sides

Chip details. Q1 is most likely a dual n-Channel MOSFET.

Oddly enough, both cells were reasonable close in voltages around 3.68 and 3.70 V upon disassembly, so the loss of capacity is probably due to excessive discharge and degradation.

Component Identification

Now for IC1 - what type of device are we looking for?

Example: Ti BQ29200/BQ29209: https://www.ti.com/lit/ds/symlink/bq29200.pdf

bq2920x Voltage Protection with Automatic Cell Balance for 2-Series Cell Li-Ion Batteries

However the package is

• about 2.0 x 1.8 mm
• DFN6 style with EP
• marked "PAJ 850"
• EP is not connected
• from a pack dating back to 2004-2006

One has to appreaciate the teardrops, but for now, identification is a 0/2.

And the common-Drain FET? A popular IC for single cell solutions is DW01A:

https://hmsemi.com/downfile/DW01A.PDF

A combination of both is implemented in the IC in question.

HY2120 "2-Cell Lithium-ion/Lithium Polymer Battery Packs Protection"

https://www.hycontek.com/wp-content/uploads/DS-HY2120_EN.pdf

A Closer Match, But Not Quite

https://eu.mouser.com/datasheet/2/294/r5463_ea-3218922.pdf

Take-Aways

• no NTCs, and thus no temperature sensing during charging
• B and D are only connected to "EB-" (external BATT-?) and among each other
• B and D just seem to form a resistive divider with a factor of ~0.75
• very basic protection circuitry, low current cell balancing
• common-drain n-Channel dual MOSFET (unidentified)
• no communication interface / handshaking