a few things to remember

[coolbreeze]

MAke sure your regulator can handle the field amp draw of your alt.
have 25% more amps avalible then what your biggest box draws.
remember that some alts can not produce the same amps at 20v at they can at 14.
do not use 2 8 v batts and try to run 20v. you will burn them up and waste amps trying to do so.