Amazon has the Schumacher SpeedCharge Battery Maintainer and Charger (SEM-1562a) for $19 with free shipping on $25+. Automatically switches to trickle charging when battery is fully charged. Compatible with 6 or 12-volt batteries. Walmart also has it for $19 with free pickup.
Sears sells a DieHard branded (http://www.sears.com/diehard-battery-charger-maintainer/p-02871219000P) one that's very similar but has a 3 year warranty and includes the CIG cord adapter ($5 - $10 value) for easily charging hard to reach batteries (BMW, etc.) and the quick disconnect harness. I opted for the DieHard and love it, although the Schumacher feels heavier and more durable.
I'm in for one (68% off) list. Pretty good reviews also.
I have one and it is a very good charger, it will also Desulphate batteries that have been sitting for a long time.
Sears sells a DieHard branded (http://www.sears.com/diehard-battery-charger-maintainer/p-02871219000P) one that's very similar but has a 3 year warranty and includes the CIG cord adapter ($5 - $10 value) for easily charging hard to reach batteries (BMW, etc.) and the quick disconnect harness. I opted for the DieHard and love it, although the Schumacher feels heavier and more durable.