#173021 is used in 71-73, 350 with T-60 or UA-1 heavy duty battery option and 71-73 with 454. These are an active unit when the batteries are received. Even though they do not need charged every 30 days, such as a lead acid, they now need to be checked with a volt meter and kept in the top 50% (we send a chart with each battery). If monitored properly they should last 7-10 years. Absolutely no fluid should ever be added to these batteries, the caps coming off are just for show. These batteries really only need a charge every 2 1/2 months, if put away at a full charge and disconnected, then 10 or 12 amp back up to full, about an hour and a half. On vehicles with alternators you can start the car and the car will charge it up. Volt meter's will become your best friend with this battery. If you want the battery dated, add part # 171025 for battery dating service. NOTE: This is a hazardous item and cannot be shipped by air or outside the Continental U.S.