Went the shape way route, fit like a glove. Max Amp changed their battery size and it still fits. A bit too snug for my preference but with a 4S I don't think I'll have to worry too much if the battery puffs. My soldering skills on the other hand are a bit rusty.
This error is very common if you have anti-ransomware enabled. Either disable anti-ransomware or create a rule to allow the installer to bypass the anti-ransomware protection