F1 vs F2 battery terminals
What is the difference between F1 and F2 terminals?
Both are flat spade tabs on sealed lead-acid batteries. F1 is 0.187 inches wide, about 4.75 mm, and F2 is 0.250 inches wide, about 6.35 mm. A clip made for one won't grip the other properly, so measure the tab with a caliper before you order a replacement cell.
| Terminal | Width | Seen on |
|---|---|---|
| F1 | 0.187 in / 4.75 mm | Some 7 Ah cells, including the listing behind ASIN B00K8V30D0 |
| F2 | 0.250 in / 6.35 mm | Most 9 Ah UPS cells |
| +F2 / -F1 | both | CSB HR1224WF2F1 T2 batterystore.com |
| NB | bolted | CSB GP12170NB T2 batterystore.com |
What does an asymmetric +F2/-F1 terminal mean?
It means one cell has a wide F2 tab on the positive post and a narrow F1 tab on the negative post. The CSB HR1224WF2F1 in the APC BE600M1 is built this way, so the leads cannot easily go on backwards. A dual-F2 replacement needs one step-down adapter on its negative tab.
When do you need a terminal adapter?
You need one whenever the tab on the new cell differs from the clip on your harness. An F1 cell on an F2 harness takes an F1-to-F2 adapter on both tabs. An adapter adds a joint and a little height, so check the door still closes before you rely on it.
What about nut-and-bolt terminals?
Nut-and-bolt, or NB, terminals appear on larger blocks such as the 17 Ah cells behind the APC RBC7. The lead bolts to the post, so spade adapters don't apply. Keep the original hardware if it is sound, tighten it gently, and insulate the wrench, because a slip across the posts is dangerous.