Walmart offers the Schumacher Electric 15-amp Battery Charger for $34.70. (Amazon charges the same, although it's currently backordered.) Opt for in-store pickup to avoid the $5.99 shipping fee. That's the lowest price we could find by $15. It features 3-amp battery maintainer, microprocessor control, start/stop interface, LED indicators, digital display, and auto-voltage detection.