Several weeks ago I purchased a pre-owned Mid 2010 17in MBP from a reseller. After a week it developed a fault: it would just dies at around 18% battery life. Coconut Battery told me it was a new battery, but it didn't appear to be genuine. To restart the MBP I would need to connect the charger and perform an SMC reset. I contacted the seller who shipped it back and replaced with a new battery, which, they say, is NOS genuine. Coconut Battery says it's a DynaPack, is 170 days old and now in its 7th cycle. The machine worked OK for a day, now it cuts out at about 8%. Not every time, but it's done it 3-4 times now. Contacted seller, who is being very good about things, and has offered to have it collected and refund me. Before I do this, I'm keen to explore all possible fixes, as it is a hard machine to relocate, and I did get it at a good price (or not, depending on your POV!). Seller has agreed to help with any remedy if one can be found. So, things I have tried so far... 1. New battery. Lowered the cut-out point, but didn't eradicate it. 2. Alternative HDD tried. No difference. 3. Tested RAM, appears OK. It's loaded with 2x4, tried running with 1x4, but no difference. 4. Checked all internal connections: as far as I can tell, all good. 5. Installed SMCFanControl. Fan activity and temp appear normal. Although, worth noting this machine appears to run a little hotter than previous models. But not excessively so. 6. Re-install OS (Sierra). No change. That's about it. Does anyone out there have any further troubleshooting ideas? Thanks.