Walmart offers the Stanley FatMax 8-amp Battery Charger bundled with an Extension Cord for $24.30. Opt for in-store pickup to dodge the $5.99 shipping fee. That's a buck under our January mention, a savings of $9, and best deal we could find. It connects with battery clamps, battery ring terminals, or a 12-volt DC plug and features reverse polarity lights that warn against an improper connection.