Macbook Pro 5,1 will only boot after multiple SMC resets I have a Macbook Pro 5,1 (late 2008) running El Capitan (10.11), which is the latest officially supported OS for that machine. When I turn it off I cannot turn it back on without resetting the SMC multiple times (sometimes up to 20 times, sometimes just once is enough). The problem only occurs when the machine is turned off for at least a few hours, otherwise it turns on perfectly. This makes me think, that there could be some kind of small battery on the logic board which drains too fast due to the age of the Macbook? It doesn't matter how much the main battery is charged.

What I've tried so far:


quick Apple Hardware Test without any results
used different RAM
used different internal HDD
resetted NRAM/PRAM
installed a new copy of the OS and then imported everything (Data and Settings) with the migration assistent


Any other Ideas? 
Thanks in advance!
I’ve seen this before and it could be one of two things (generally speaking):


failing power supply 
failing/failed SMC chip


When I mention "power supply" it can mean either the physical power supply like that in a Mac Pro (workstation) or the circuitry on the logic board of a MacBook (laptop) that manages where the current is sourced from - battery or external adapter.  There's power that goes to the SMC so that it can handle how and where power is distributed throughout the logic board.

It wouldn’t be a battery because when power is removed from an SMC chip, it actually resets.  So, resetting an already reset SMC wouldn’t do anything as you’ve demonstrated with the other numerous resets. However, what we have to remember is that when an SMC reset occurs, the whole system is being reset (warm power cycle). 

The power supply (circuitry) could be failing in that not enough current is getting to the correct power rails until finally there’s enough capacity to get it to work; there could be dry solder contracts on any of the SMC components including the chip itself; or it could just be dying. 

The least expensive DIY test you could do would be to replace the power supply with a known good one (if on a workstation), next followed by a replacement of the logic board.  Unfortunately, to get a proof positive diagnosis, you’d need high level told like an oscilloscope to accurately measure the power going to the individual power rails. 

Ultimately, you'll need to send it in for service because there's nothing more that can be done from a DIY perspective.