battery not recognised, replaced battery. cannot smc reset

Hello have been trouble shooting this problem for a while now. Starting from the beginning:

just to note I keep my Macbook in impeccable condition so none of the issue are due to anything like water damage or mistreatment however it is used heavily as I use it as my machine for music production and have used it heavily for the past 2 and a half years.

The first problem i have is that my left shift stopped working out of the blue a few months ago. This means i cannon smc reset, i have been told to use an external keyboard but this doesn't work as it has to be the built in keyboard. removing the battery and holding the power button also doesn't work on this model.

The battery icon suddenly had an X on its symbol and started to say not recognised. When the macbook is shut down, if i try to turn it on again the light on the front will light up and the fans will give a very gentle whir but absolutely no response no matter how long it is left. However if i force shut it down out of that state and just leave it to sit for an hour i can then turn it on fine. The battery shows a percentage for about half an hour (plugged-in and also when not plugged-in) then will return to the state of not recognised again. If i leave the charger out for more than about 20-30 mins the mac will shut off without warning, however will stay on fine if i have it plugged in by the charger.

following on from this, i have purchased and fit a new battery. This has definitley helped the laptop but diddn't solve the problem at all. I know i need to smc reset however have no physical way to do so without my shift key working. Is this likely to be a keyboard replacement to fix? Bearing in mind the only key not responding is the left shift and it came about from absolutely nothing just one day stopped working.

I am more than happy to undertake all work on the mac myself so any suggestions of what may need replacing or doing would be great. The macbook has always gotten extremely hot which apple have always just told me is the way they are, and had to have the motherboard replaced by warranty previously as the headphone port decided to pack in after a couple of months.

Hope someone can help is most appreciated ! hope all have have a good christmas