MacBook Pro 13" 2017 won't boot from battery
Primary problem is that after replacing a very tired battery with a replacement from iFixIt, my laptop will not boot from battery anymore. It gets to about 40% of the progress bar and fails. When booting with the power cable in, the screen flashes brighter at this point, before continuing to complete the boot cycle.
I have removed, cleaned and reseated the connections for the battery board to the motherboard, but this has not helped.
Coconut Battery reports that my 'new' iFixIt battery was made in Nov 2013, making it twice the age of my laptop! It also says that is capable of only 64% of it's design capacity.
Have tried multiple SMC resets and a full factory OS reinstall, but no change to these 2 core issues.
I'm thinking I either have a dodgy connection to the motherboard or a dodgy replacement battery, but I'm not sure how to determine which it is?
Adding images showing Coconut battery readout with and without power. Potential capacity at full charge is showing a much higher figure than earlier today, albeit still poor for what should be a new battery. I have been seeing wildly varying figures for % of design capacity it thinks it can achieve.