I recommend a high frequency charger harborfreight sells one for about $20.00 http://www.harborfreight.com/15-amp-thr ... 99857.html
and Lowes has one for about $30.00 http://www.lowes.com/pd_328609-89606-BC ... facetInfo=
Either one will suit your needs for most batteries. High frequency chargers break down the solids (sulfate) that causes batteries to become unusable because it coat the lead and prevent the battery from charging. If the battery is flat stone dead these chargers won't work as another poster pointed out. If any of you want to make your own simple desulfator here's the link http://poormanguides.blogspot.com/2009/ ... fator.html
and for a couple of bucks I have a limited amount of capacitors available. This one will charge even dead batteries as long as they aren't completely sulfated.