my civic seems to be low on electrical power lately, i put in a new battery, and now when im driving at nite, when i let go of the gas and the RPMs drop, the lights dim a little. i had the battery tested and it's fine, i think the alternator may be goin. other than that, no idea.

i was considering adding a second battery, since i wanna put in a system soon. how do i go about adding a second battery ? can the stock alternator power 2 of them ?