is there any harm in having two battarys hooked up, ethier the 2nd one in the drivers side or in the boot, as ill be running subs and speakers all round all run by there own amps ie front, back, sub wondering should i need a bigger alternator or will the oem one keep both charged, or will i run in to touble with having them both half charged and as good as a bigger one from say a 5 diesel?