Something else to consider, especially for those using flooded batteries, is an anti-corrosion mat. NPD stocks them under PN 954-1A for under five bucks. You simply cut it to fit your tray and place it under the battery. If your battery leaks or over flows from overcharging, the mat will absorb the battery's electrolyte and minimize damage to the battery try and fender apron. That's cheap insurance in our books!