Black & Decker's BM3B 6V and 12V Battery Charger / Maintainer, Schumacher's SC-1200A/CA, and Battery Tender's Junior 12V Battery Charger all have generally positive reviews on Amazon.com. As of June 2015, the prices for these items range from $19.99 to $34.39.
As of June 2015, the Black & Decker BM3B is the least expensive of the three. The Schumacher SC-1200A/CA is the most expensive. Both can charge 6V and 12V batteries and have float mode monitoring. Battery Tender's Junior 12V Battery Charger can only charge 12V batteries. It is also capable of float mode charging, but does not feature float mode monitoring.