Kobo Sage e-reader tricks

Originally published on 2025-03-06, 2 min read, ~500 words.

Since about a year ago, I have been using a Rakuten Kobo Sage as my e-ink document reader. Overall, I’m OK with it, except for the abysmal battery life. Yet, it makes up for that with some nice features, like high screen resolution, high contrast and an adjustable backlight. You can adjust both the brightness and the tint of the backlight, which is important to me. However, I’d like more precise control in the lower brightness range and an even more reddish tint. In addition, the Kobo Sage works very well with the open-source alternative firmware KOReader.

Here, I’m going to collect tweaks related to this e-ink reader. For now, I have only replaced the battery in the PowerCover. I will update this article if I do anything else.

Replacing a broken battery in Kobo PowerCover

After I bought my Kobo, I looked for some kind of cover to protect it during transport. I spotted a very cheap Kobo PowerCover, model N779, on OLX with a broken battery. A cover with an integrated battery seemed a bit strange to me, but it’s probably meant to mitigate the terrible battery life.

Close-up of the markings on the cover, model N779.

Since I initially wanted just a simple cover, I bought it promptly. I didn’t care about the battery, as I thought I would never use it. However, the battery life of my Kobo Sage turned out to be unsatisfactory, to put it mildly. So, I investigated whether I could replace the cover’s battery, which turned out to be easy.

The PowerCover's backside. Two halves are glued together with non-drying glue.

Prying open the cover with a piece of hard paper.

The device is open. Visible patches of non-drying glue on the plate to the right.

The cover is held together by non-drying glue, it is very easy to pry open. I used a piece of hard paper, but a cheap plastic toolset for opening smartphones would be even better. The original battery had the following markings:

Rechargeable Lithium-ion Battery
Model: PT158098 (1ICP2/80/98)
Voltage: 3.7 V
Rated capacity: 1200 mAh
Max charge voltage: 4.2 V
Manufacturer: Guangdong Pow-Tech New Power co., Ltd.

The marking 1ICP2/80/98 indicates that the battery is a single-cell lithium-polymer with dimensions of 98 × 80 × 2 mm.

The electronics inside the PowerCover: 37NB-0K25AM+2A0.

The original, dead battery: PT158098 (1ICP2/80/98).

Testing the cover with a different 3.7 V battery of similar capacity.

I measured the voltage of the old battery, and it was completely dead — 0 V. To check the electronics, I soldered a random 3.7 V Li-polymer battery I had lying around. To my surprise, the cover started charging. BTW, when the cover is connected to the Kobo, KOReader displays separate battery levels for both batteries:

KOReader showing 100% main battery and 23% cover battery.

I found a replacement battery on Aliexpress for about 13 euros. A replacement arrived a month later, strangely with no markings at all.

The old battery is glued to the cover, and since it is very thin (2 millimeters), its deformation is almost inevitable during removal. Warning! Li-ion batteries may catch fire or explode if deformed, punctured or otherwise damaged. I advise ungluing it outside, wearing protective gloves and goggles.