I received the battery kit for my 2018 MacBook Pro and as per the above comment from bcardanha - Oct 12, 2021, I checked the voltage on the pads marked + and - . It was zero volts so I panicked a bit.

I sent a message on the iFixiT Facebook page and I got no reply. I finally found the customer service email for Ifixit Europe and sent them an email voicing my concern as I was not keen to work for couple of hours just to discover that the battery is faulty. I had an almost instant reply on the email (kudos to them) and they adviced me to go ahead and install the new battery as the voltage measured when battery is not connected is not relevant.

I took a leap of faith and after two hours… the new battery showed 50% charge and everything seems to be working just fine. I am happy it worked.