Battery is not seen, charged

hi there!

i have a problem that is quite persistant! the battery is not seen nor charged anymore by the lap top. also the computer cuts out at unpredictable times. i have two in principle working batteries (one new, the other fair) and the problem is the same. when the mac goes to sleep, sometimes i can't get it to start up anymore. i have to take out the mains, change the batteries and then the green light on the lead will function again. at first it starts in red, making out 'calculating' the battery, and then it goes to an X in the battery indicator in the right upper corner of the desktop but feeds on the mains. of course i have checked the problem on ifixit! it could have been the battery connector, changed it to no avail. then another suggestion: the left I/O board, changed it, also to no avail. the logic board was replaced by apple last year (could it be the logic board again!!??). now i feel out of options. has anyone any idea cq another more helpful suggestion?

thanx!