The reason for the difference is to accommodate the different sized wire lead connectors that accompany a variety of electric-powered devices, whether they be Honeywell alarm control panels or electric wheelchairs. These terminals are flat, metal tabs that sit at an angle to the battery casing. This is where the positive and negative spade wire leads hook up to the battery. Battery power is sent over these leads to provide power to the device in question.
F1 terminals are 3/16 (0.187) inches wide. They fit into the corresponding F1 connectors at the end of the wire leads for the device they're powering.
F2 terminals are 1/4 (0.25) inches wide -- about 1/16 of an inch wider than the F1. They fit into the corresponding F2 connectors on the wire leads that connect to the particular device they're powering.
There are also adapters available that can make the F1 terminal compatible with an F2 connectors, and vise versa.
