My 2010 (OLD!) 17in Macbook Pro has always cut-out randomly for no apparent reason when not running a genuine Apple battery. I've finally worked out why and it's not the battery, per se.
About three years ago, I bought an older 2010 Macbook Pro, vintage 2010. I went to that old because I wanted the biggest possible screen: 17in. And this seemed like the last time they made one that was still readily available.
When I bought it, I knew it needed a new battery, but ran with the original it came with for a while anyway. After adding in an SSD and maxing the ram, it was a workhorse; HUGE screen, plenty powerful for my needs and cheap.
After a while I got a new battery, not genuine but not a cheapie off eBay either, but then the problems began; when on battery it would just cut out for no reason. . There seemed to be a regularly moving consistency to it. Sometimes the battery would get to around 20%, and it'd cut out. Sometimes 84%, other times somewhere in between. This would be consistent, in that it would cut out at around 20% for a week or so, then the cut-out point would move.
This pointed to either logicboard, or power supply, or loads of other things. None of which I was interested in fixing, as this machine served one purpose: For me to work at on the rare days the sun was out, and I was able to work in the garden. I found that on power it worked fine, so just made sure it was always plugged in.
A year later, four days before a worldwide trip lasting a month on which the MBP had to come because it was to be my daily worker, it died. Fuck! I sent it to the repair shop and bought a Macbook Air for the trip.
On my return the repair shop said in the month they had it they ran every test they could think of, no faults in the hardware showed up, but the replacement battery was dead. So we surmised that was the issue. So I bought another replacement, non-genuine. No fix, still dead. At this point, I put the machine away and forgot about it and went to using the MBA for garden duties.
A while and I spotted a genuine Apple battery for sale, so bought it, fired it in and boom, it's worked perfectly. Happy days. All went well until that battery started to expand (noticeable because the trackpad was getting harder and harder to "click". So once again, I was back in the market for a replacement.
Genuine batteries are impossible to get now; the machine is now ten years old. So I bought one from a reputable worldwide seller, with a very strong and well-respected brand name. It fired it up, but the random shutdowns were back, but this time at around 90%, so mostly useless.
Over the years with this issue, I'd Googled for hours but never found a fix, so it was back to using it on power. Then, the other day, on battery it cut out. Again. (I'd forgot to plug it in). When it powered back up I noticed for the first time it didn't chime, then I saw the screen brightness keys didn't work. Odd. So I rebooted it, and the chimes occurred, and the keys worked. Intriguing.
This gave me more to investigate, so off I went. After a while, I found talk of issues with this generation of machines having problems switching between graphics cards when in use; it has two: Integrated and "discreet", which is a silly name for a graphics card. The Macbook switches between the two depending on the workload, and crucially... Whether it's on battery or not. If it's on battery, it uses the integrated where possible.
Could this be the root of my issue? As it only attempts to use the integrated graphics chip on battery and it's known to have issues switching, coud this be why my problems only occur on battery?
Reading a bit further, I learnt about the option to turn this graphics switching on or off; it's done in the power setting (see image).
I noticed it was ticked, then, just as I spotted that, the damn machine shut down... I was on battery, again, and forgot.
Power supply connected, fired the machine up, back to the settings... The option to switch off the card switching was gone! WTF!
I rebooted the machine entirely, and the setting returned. OK, this is getting interesting, this is clearly connected to the issue.
More Googling and I discovered that this issue if not uncommon, the discreet card in some older MacBooks do give bother and can cause all sorts of problems. Plus I found that using the option in settings to disable the card switching isn't too reliable. Thankfully someone has made a solution; it's called GFXcardStatus. This is a little app that you use to use either of the cards permanently.
Installed it, tested it... Bingo: No more cutting out. Three years after getting this machine, and countless times thinking of scraping it a free app from the internet seems to have fixed all my woes.
So, if you are having similar issues, give gfxCardStatus a try, it might fix things.