MacBook Battery not detected

Usually if the battery is not detected, it will be due to a defective battery as the battery is the weakest link. A third party Lithium-ion battery is even more likely to be defective since the quality of third party Lithium-ion batteries is extremely poor even when purchased from a reputable vendor. The next most common cause is liquid damage to the Logic Board.

The best source for a third party Lithium-ion Battery is OWC or iFixIt (I would go with the former). Both vendors provide instructions with OWC providing a video guide as well. FYI, it is not easy to remove a battery since it is glued to the underside of the palmrest & trackpad. Most instructions have you use an adhesive remover which can easily damage the other components in the laptop, especially the Trackpad since the Trackpad cannot be removed until the battery is removed. Plus the battery is extremely fragile when removed because it is only held together by thin fragile plastic flex cables. In addition, you must make sure to keep the old battery stored safely and have it recycled.

jack3030 wrote:

Is it safe to assume my undetected battery is fully discharged?

No.

If not, how might I accomplish that, given that I cannot boot nor run the machine without AC power?

There is no way. Just be careful not to puncture the battery (don't use any sharp tools around the battery to minimize a puncture and use a nylon stick/spudger to disconnect the battery...if a metal tool punctures a battery it may produce a spark which could ignite if a significant charge remains). OWC provides video instructions which I highly recommend to review to see the process. Keep in mind it will look much easier than it really is. People have damaged their laptops doing this themselves (damaging the Trackpad, Logic Board). The battery cells have no support once removed from the case as they are only connected by thin fragile plastic/mylar flex cables so you must be careful to support the cells so they are not pulled apart. You also have to consider how to safely store the removed battery and have it properly recycled as it contains toxic materials which are combustible if there is enough charge remaining.

The battery’s meter might show zero for example but basically all that means is there’s not enough voltage available to power the device. So no the battery is likely not fully discharged and could have quite a bit of “juice” left in it.