I want to thank you for all your help.
I talked to Randy Bush at Essence Maserati in Hurst Texas. What an expert he is about these cars. He said you need a battery charger that puts out 8 – 10 amps and charge the battery through the fuse box.
The cigarette lighter circuits will not charge the battery.
So, open the fuse box, inside you’ll see a large diameter red wire that is clamped into a bus bar. That area is very tight and I was nervous about the battery charger clamp staying on, so I placed a very thin piece of wood between the battery charger clamp and all the fuses and circuit boxes next to the bus bar. When I started I had 5.6 volts in the battery. I charged for 6 hours and checked the battery, 12.2 volts. That was good. I tried the trunk and it would not open. The car started and I let it warm up to temperature. I tried the trunk again and it didn’t open.
Now this is information I haven’t seen in the Operators Manual. When the voltage gets low, the computer system starts shutting down various systems to save the voltage. That is why the trunk didn’t open. So, you need to reboot the computer, and you do that by taking the key fob and manually locking the driver’s side door with the key. When I did this the anti-theft LED did a lot of blinking. Then I unlocked the door with the key, and I was able to open the trunk !!