En 
SvPoor connections
If you have a poor connection, more batteries won't help.
Poor connections, corroded cables, or faulty battery isolator diodes mean that after just a few days you can already be down to dangerously low levels.
The lifespan of the batteries can become very short if the charging system is not working as it should.
So go through your electrical system and replace all cables that look like the ones in the pictures.
