I have had a 6v/12v regular battery charger from Sears for about thirty years now. Use it to charge a dead battery or to provide power when I am testing 12v items like my air supply pump (which does not pump) for my 81 300SD. You turn the knob for up to 24 hours for a charge; however, in addition to being a multi-hour charger, at the end of the hours marks it actually turns out to be a trickle charger. Has never failed me and I highly recommend it.