Two different MacBook Air 13 e2015, both shuts down with 46% battery left

Reset the SMC for both Macs: How to reset the SMC of your Mac

Both are, usually, plugged to the power line and occasionally unplugged for just 1 to 3 hours, never until battery completely depleted.

If you want them to last for a long time, batteries need to be used regularly. If their power adapters are usually connected, disconnect them and use the Macs on battery power alone every once in a while. Once a week, at least. Read About Mac notebook batteries - Apple Support.

Model:MacBook Air 13” Early 2015

OSX: El Capitan

Battery Condition: (“About this mac:->”System Report”->”Power”)

Cycles: 41 (Great!)

Charge level: 6700+ mAh (Spectacular!)

Voltage: 8.2+ Volts (7.4V nominal Li-Ion, but this is in line with a fully charged battery...Marvelous!)

Charging current: 500mA or less. (Less than 4W!) Not good...

Status: “Replace Now” (This is incorrect, see below)

Symptom:

Power cord must be plugged in to start.  Charging is incredibly slow.  Kill-a-Watt shows that a 45W capable charger

is only delivering roughly 10W of power with less than 4W going into the battery.  Plug remains amber even when at

full charge.  

Resetting SCM with power on will result in green light on plug, which returns amber within a few seconds of releasing SCM reset.

Generally removing the power plug with laptop on will cause Mac to shut down.  Occasionally(rarely), plug will be green and removing plug at this time will not shut down laptop, but if is laptop shutdown, the plug will be required to restart.  SCM Resets and PRAM resets were ineffective at addressing the issue.  Charging current readings through OSX were not entirely reliable, and in some cases showed battery charging when no power supply was connected, for the few instances I could get the laptop to run without cable.

Solution:

Tools: P5 Pentalobe driver (reference Wiha Master Tech 65 Piece Set - ESD Handle, Mini Ratchet and MicroBits In

Metal Storage Box)

Power cord disconnected.  Back panel of MacBook was removed using P5 driver.  Battery connection pulled out from connector.  Logic Board (PCB with MagSafe connector) had visible flux residue.  Isopropyl Alcohol and toohbrush used to clean

board.  Liquid mopped up with rag.  Cleaned and wiped a second time.  Reassembled and now it works.  Most likely flux residue caused leakage which interferes with measurements of battery currents.  SCM decides that battery is bad when it is completely fine.  Leakages might also explain odd charging current readings from OSX.  This is a manufacturing defect as it is clearly

the case that the main PCB is pristine, as the logic board should be.

Final Test Results:

10 power cycles and laptop works fine. 

OSX now says battery condition Good.

Charger connected and disconnected 5 times and Kill-A_Watt indicates 45W of charging. 

Power cord light turns green when charging complete.

Correction: P4 Pentalobe to remove back panel not P5