iFixit Replacement Battery Charging Very Slowly

I have a 15” 2011 MacBook Pro which runs macOS Catalina 10.15.7 (I have replaced the logic board with that of a 2012 model). I recently ordered a replacement battery for my MBP from iFixit. The battery was manufactured fairly recently (about 165 days ago). I calibrated the battery as soon as I received it and it has a couple of cycles on it now.

The issue is that it takes a really long time to charge the battery (e.g. 8 to 10 hours). According to coconutBattery, the battery is charged with about 40 Watts of power when it is closer to 0%. The power gradually decreases as the state of charge increases. At 95%, the power is around 4 Watts.

The MPB uses an 85W power adapter. According to iStat Menus, the “System Total” power is around 17W (because I am using an external display). Therefore, there is room for the charging circuitry to draw more power (85W - 17W = 68W). When I put my machine under a more CPU-intensive workload, the total “DC In” power becomes around 75W so I assume there are no issues with the adapter (I have also cleaned the MagSafe port to ensure there are no issues there).

Here are some other things I have tried to address this issue:

• Reset SMC
• Reset PRAM
• Repaired disk permissions

I have seen a few similar posts on the forum but not many of them had this level of detail in them. Therefore, people had suggested changing the adapter or the logic board may help. In this case, I suspect the issue is not with any of the two.

I was wondering if anyone has ever faced a similar issue and can give me pointers to what I should further investigate.

Thank you very much.

P.S. This new battery is a replacement battery for another battery I received from iFixit a week ago. That battery was charging very slowly too, but it had other issues and I had to request a replacement.

EDIT 1:

Here is a screenshot from coconutBattery.

With the iFixit batteries, my MBP does not wake up from a deep sleep. I have to press the power button to turn it on. Then, I get the following error from the OS when it turns on:

“Sleep wake failure in EFI”.

By disabling the deep sleep mode, the issue goes away.

EDIT 2:

Based on Dan’s answer, during the SMC adjustment period, it is perfectly normal for the battery to be charged in 10 hours or so. I will update this question in about a month and will report the 0-100% charging time.

EDIT 3:

Unfortunately, the second battery kept charging very slowly and faced issues similar to those of the first replacement battery, e.g. “Sleep wake failure in EFI”.

While I’ve had a good experience with iFixit most of the time, it didn’t work out well this time.

I ordered a replacement battery from macsales.com and it seems to be working as expected. It takes around 4-5 hours to charge the battery from 0 to 100% and I haven’t experienced any sleep wake issues yet.

Another interesting point about the macsales.com battery is that it’s design capacity is 7800 mAh, much higher than that of the OEM and iFixit batteries. The downside is that the temperature goes up to 30 degrees Celcius while the OEM and iFixit batteries go up to 27 degrees Celcius.

Another difference is that the iFixit battery has the holes for screws in the right place and replacement is very smooth. With the OWC battery, the rightmost hole doesn’t align well and the screw has to be placed at an angle and with a lot of force.