I suspect there is a charging system problem that is contributing to the failsafe. You need to get the charging system properly diagnosed.

If you don't have one purchase a multimeter so you can check battery voltage, monitor alternator output and check for parasitic drain. That is next step.

so, great idea on monitoring voltage from the odb. This is where as a very new person here- say the obvious!

It started at 14.2v when idling. I drove for a couple minutes and it dropped to 14.1v. it randomly jumped to 13.8 for under a second.

At idle:

15 minutes 14.0v

20 minutes 13.9v

25 minutes 13.8v

30 minutes 13.6v

35 minutes- drove it for a couple minutes, jumped around a bit 13.9 to 13.5

So seems the voltage is VERY slowly dropping... Is that normal?

What should I check?

As for the multimeter/parasitic test- shipping will take a while. In the mean time, I plugged in my old battery and charged it on jumper cables. It also triggered the trans fail-safe. Is it unlikely both batteries fail the parasitic test?

Really don't want to kill the new battery! What can I do to avoid this?

Sounds normal to me. The system will work fine with 12.2 or higher voltage.

As for the battery 12.6 is full. So as long as the voltage is over 12.6 running its not going to bother the battery any. As long as its over 12.8 its actually charging the battery too.

For your purposes your good to go alternator wise I imagine.

On a side note for future references the voltage shown in the dash reading is not accurate to actual power. I use a cigarette lighter volt meter to keep up with actual readings from time to time. The dash readout is higher than actual voltage. I need to see if I have a pic of that thing.

You still need to get a volt meter for testing things like your cig lighter for example that your having problems with.

Alternator seems to be working properly. Turn on the bright lights, radio and heater fan on high and see if the voltage increases.

This isn't me but its the same meter I have. Super reliable.

https://www.youtube.com/watch?v=nLLJ4BeTzO4

Here it is on Amazon.

http://amzn.to/2gHftnZ

I need to order one for each car now that I think about it. I have been walking these between cars as needed.

Oh one last thing :)

Don't leave it fully plugged in when not in the car. It keeps running though it would take a very long time to run the battery down. I just pull the meter out a tiny bit when not in use and leave it in the cig socket. When I want to monitor voltage I just push it back in some.

As I mentioned, volt.meter will take a while to be delivered.

What else can I test without the voltmetre? EG can I remove fuses and see if it helps?. Anything I should check/tighten?

Should I unplug the negative cable of the battery while I'm not fixing the car to maintain the battery?

The opposite of this happens! The voltage decreases- from say 13.8v to 13.4v.

What does that mean?