MacBook Pro 15" 2011 A1286 stuttering and slow

Hi all,

I have a problem with my MacBook Pro 15”, late 2011 with AMD Radeon HD 6770M dedicated video card and Intel HD 3000 integrated card

I use the computer occasionally at home and a few weeks ago I noticed that the battery was charging very slowly, I changed the power supply with a new original one and the problem remains.

I also changed the battery to a compatible one and the problem persists. Now for a few days I have also noticed that the computer after a few minutes from starting it jerks and becomes very slow.

However, this problem arises in several ways:

• With the battery attached the problem is always from startup, if I try to enter safe mode the Mac shuts down at the end of loading.
• If instead I disconnect the battery, the computer starts, sometimes it doesn't become slow while other times after a few minutes it starts to jerk and become slow.
• In Safe Mode for the moment this problem doesn't seem to exist (without battery) In normal mode, when the machine doesn't lag I tried to do a GPU test and it works fine, so I assume it's not a video card problem.

UPDATE: If I do the SMC with the battery connected, the problem disappears for a few seconds or 1\2 minutes and then returns.

Do you have any suggestions? Thank you!