Check fusible links. The battery was protected by a fifty amp fusible link. The car wiring has a 30 Amp fusible link that is buried in the wiring that comes out through the fire wall below the master cylinder and traverses the top of the fire wall to get to the alternator.
If your battery has no charge that means it isn't being charged. The nominal 12 volt lead acid battery when fully charged should read 13.6 volts. Your alternator has to out put more than this to charge the battery.
Second problem is when you put the battery in the trunk you lengthen the wire. Wire has a natural resistance to current flow based upon the length and the diameter of the wire. the bigger the wire gauge the less voltage is lost. If you are charging the battery from the front of the car you need to increase the wire diameter to handle the voltage loss per foot and the current flow through the wire.
Back in the early sixties while copper ore was easily found and mined by open pit mining the wire gauge on the alternator was 8 gage and the battery used 00 gauge cables. By 1967 copper had doubled in price as supply dwindled and the size of the wires got smaller even though the amperage load of newer cars increased. The alternator gage dropped to a 10 gage wire and the battery cable shrank to a 4 gage cable. Today virgin copper is hard o find as most wires are made over seas from recycled scrap that is far from virgin copper.
Here is what I used to wire my battery in the trunk of my Impala.
Screw on battery cable terminals from Taylor wire.
Moroso through panel battery terminals to jump or charger in the pits:
Moroso 200AMP disconnect switch (required under NHRA rules):
Taylor 01 gage battery cable:
Ground and battery leads joining the cars wiring on the fire wall:
Note the black ground cable that comes up from the frame to join my Ford solenoid that starts the motor and compare it to the factory black ground battery cable to appreciate the increase in size of the cable.
If your wiring is too small to charge the battery you can use a higher voltage alternator. There are 16 volt (as opposed to a 12 volt) GM alternator used on race cars with a battery in the trunk.