there could be two reason:- (1) Battery itself has started malfunctioning as surfacepro 4 batteries available in market are not upto that standard and stop working. its not easy to get a right battery for surfacepro 4. I have gone through this problem. replaced 100s of batteries in surface devices but always had problem with pro4 batteries. (2) Motherboard issue- While replacing battery a isolating diode (that isolate adapter power and battery power and power up the device in absence of adapter) gets burnt out most of the time. then device stopped recognizing the battery. Need to replace the diode in this case. better to contact a person who know more about surface devices.

Definitely a bad battery. Check the voltage a battery board connecors if you are getting 12V or More than logicboard is good. it happens some time with aftermarket batteries.

It could be a internal issue. Most probably liquid or moisture damage on the logic board. as it is quite old model, this is very common in macbooks. its better to get it diagnosed by a technician. i have repaired hundred of macbooks with this problem.

try to fix it yourself. make a epoxy of thermocoal and superglue and put in between frame and hinges. in few minutes it will be hard solid.