#173021 is used in 71-73, 350 with T-60 or UA-1 heavy duty battery option and 71-73 with 454. #173020 and 173021 can also be used as a replacement for 74-75's.
Maintenance free means "no fluid" is needed. It does not mean that it can sitand not be charged. 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 small charges or maintainers should be used on the 12 volt batteries, they will reset the memory of the battery and without revering the process 2/3 of the battery will never get a charge and will deteriorate.
* Absolutely no larger charges, boost or any charge over 15 volts on a 12 volt, and no higher than 8 volts on a 6 volt AGM's*. This will cause the AGM* battery to release pressure by popping its buttons, and will leak in the