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trurle · 08-16-2024, 09:18 AM

thanks for posting this. I wish I had found this before I started replacing the battery in my nova 3.

my original battery did not last long either and made the book behave erratically. looking at the battery, it doesn't surprise me, it seems of very poor quality. the thickness of the original battery is not 2.5mm, it's ~3.6mm.

I opened the case by carefully inserting a wide thin stanley blade and prying slightly just enough to put the thin plastic lever in the gap, then carefully moving it around the case. since the original battery was fecked, I used a thin flexible filling knife to gradually bend and separate it from the frame, but be very careful of the two flexes that go underneath it.

as for the replacement, I took the same approach and started looking for other mass-produced batteries for tablets/ereaders as I don't trust cheap compatible batteries from aliexpress. unfortunately I did not find MC-308695/ST28 and opted for MC-347993/ST08/58-000084. Its dimensions are 78x93x3.5. I measured its capacity and it was true 3500mAh.

as it turned out, the protection circuit in that battery is set to cut-off at 4.2V (I forgot to check that the original battery was 4.35V), which meant that the reader wasn't able to reach full charge (cycled between charging and charged, stuck at 86%). It would work of course but annoying nevertheless. so I removed the protection circuit and replaced it with the one from the original battery. I understand that the new battery may not be specced for 4.35V but in my experience all mass-produced li-polymer batteries are these days, and after charge is complete, the battery holds this voltage, which is a good sign. I will keep an eye on it heating up or puffing.

another problem with ST08 is that it's got a 47KOhm NTC, so replacing the protection circuit solved that problem also.

BTW the OP suggested MC-308594 is also 4.2V (judging by the label), and it's worth checking the NTC is actually 10KOhm.

next time I am going to use MC-308695 as this seems the best fit (although lower capacity).

08-16-2024, 09:18 AM	#6
trurle Junior Member Posts: 1 Karma: 10 Join Date: Aug 2024 Device: onyx boox nova 3	thanks for posting this. I wish I had found this before I started replacing the battery in my nova 3. my original battery did not last long either and made the book behave erratically. looking at the battery, it doesn't surprise me, it seems of very poor quality. the thickness of the original battery is not 2.5mm, it's ~3.6mm. I opened the case by carefully inserting a wide thin stanley blade and prying slightly just enough to put the thin plastic lever in the gap, then carefully moving it around the case. since the original battery was fecked, I used a thin flexible filling knife to gradually bend and separate it from the frame, but be very careful of the two flexes that go underneath it. as for the replacement, I took the same approach and started looking for other mass-produced batteries for tablets/ereaders as I don't trust cheap compatible batteries from aliexpress. unfortunately I did not find MC-308695/ST28 and opted for MC-347993/ST08/58-000084. Its dimensions are 78x93x3.5. I measured its capacity and it was true 3500mAh. as it turned out, the protection circuit in that battery is set to cut-off at 4.2V (I forgot to check that the original battery was 4.35V), which meant that the reader wasn't able to reach full charge (cycled between charging and charged, stuck at 86%). It would work of course but annoying nevertheless. so I removed the protection circuit and replaced it with the one from the original battery. I understand that the new battery may not be specced for 4.35V but in my experience all mass-produced li-polymer batteries are these days, and after charge is complete, the battery holds this voltage, which is a good sign. I will keep an eye on it heating up or puffing. another problem with ST08 is that it's got a 47KOhm NTC, so replacing the protection circuit solved that problem also. BTW the OP suggested MC-308594 is also 4.2V (judging by the label), and it's worth checking the NTC is actually 10KOhm. next time I am going to use MC-308695 as this seems the best fit (although lower capacity).