Let’s Replace the Battery in ONYX BOOX MAX: Episode 2 - Attack of the Charger

ONYX BOOX MAX e-reader

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After replacing the battery, the reader happily worked for a couple of weeks and reacted with a light while being charged. But suddenly, it started to show the ‘Low Battery’ message. My initial guess was that the mainboard (and OS) somehow can’t get the feedback from the battery to figure out its current charge level (as I ignored the white wire while connecting the new battery), but still charges it. So, I thought it should continue to work even though some software counter in the OS would eventually show the 0% charge.

And the day has come: the reader turned itself off showing the low charge level image. It didn’t load when I pressed the button. And to my surprise, it did not boot even when I attached the power charger: it went into the infinite boot loop and showed the blue light.

Googling on the Internet wisdom database showed that:

the 3-wire battery should ideally be substituted with the 3-wire replacement
if the replacement is the 2-wired one, then:
- option 1:
  - measure the resistance of the grid between the ‘-‘ wire and the controller wire in the original battery
  - solder additional resistance element (with a value comparable to the one measured above) while wiring up the replacement battery
- option 2:
  - reuse the 3-wired charger board of the battery

Since I hadn’t got rid of the original battery and option 1 looked too complicated, I decided to follow the way #2.

My amateur journey:

take the original battery and detach the small charger board from it
disassemble the reader (see Episode 1)
solder the charger board into the circuit
attach the charger, check, and see that the behavior has changed: now it’s the red light!
assemble everything back together
attach the charger and try to load the device: it boots
leave it for at least half an hour to charge the battery a bit: it now better shows the charging process in the OS
turn off the charger and verify that the reader works from the battery
voila