Normaly a trickle charger is 1 to 2 amps or less for automotive batteries, and 1/4 to 1/2 amp for large motorcyle batteries, riding lawn mowers, and other batteries that you might have sitting over winter.
I think your civic has around 45-50amp hour battery, so assuming you a loss of 20% in heat a 6amp charger should have a low battery fully charged in about 10 hours, less if it's not fully discharged.
A few things to check: the cables that connect to your battery should be clean and snug, if they are not snug then you will have simaler simtoms as a dieing battery, if they have alot of oxide on the connections you can get a nifty little brush for cleaning the posts and cables from any auto parts store.
Next! check the water/acid leavle in your battery, unless it's a sealed battery it should have a cover on the top of it, while wearing old cloths and safty glasses (battery acid gives chemical burns to skin and clothing) if you pop that off you will find 6 holes, with a flashlight carfully look in to each of those holes and make sure that the water based acid is above the leavle of the lead plates, if it is not then very carfully add distilled water (never tap water as it has minerals that will kill your battery), this should bring a bit of life back to your battery and make it last longer.
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