How many amps to start these things?

[86jetta1.6]

I have batteries (Group 31 AGM's 1000CCA) relocated to the trunk on two of my jettas, I also mounted on board chargers (40A marine style) in the truck that is wired with the block heater, when I plug my block heater in, it also charges my batteries. I have found this EXTREMELY useful in the winter for starting OTHER vehicles. I cant tell you how many times it has come in handy. Hook up jumper cables, then plug my car in while trying to jump the other vehicle. I ran 4/0 wire from trunk to starter and ran ground in trunk to upper seat belt bolt in trunk. Also ran 4/0 jumper from chassis to engine block. Its total overkill but when it was -10 all winter I never had an issue.

Also, I tested my car in fall with an Ammeter and my starter was drawing about 345 amps on a car with 225k miles and about 300psi (low) compression.