Stanley FATMAX 18V Battery Adapters
The older Stanley FATMAX 18V platform, not the FATMAX V20 range that replaced it. The two do not fit each other, so check your battery before you order.
The packs are getting hard to find and the tools still work. 1 adapter let a current battery run them.
Pick a tool to run from your Stanley FATMAX 18V (Old) battery
Stanley FATMAX 18V (Old) questions
Why do some batteries say 18V and others 20V?
They are the same class of battery, measured at two different moments. Five lithium cells in series read about 20V fresh off the charger with nothing drawing from them, and settle to about 18V once a tool is running. A brand that prints 20V is quoting the first figure and one that prints 18V is quoting the second. That is why an adapter between an "18V" platform and a "20V" platform works: there is no conversion to do.
Will this fit my other Stanley batteries?
Only Stanley FATMAX 18V (Old) batteries. Stanley also sells Stanley FATMAX V20, and those use a different socket — same brand, different rail and terminals, so they need their own adapter. Compare the sliding rail on your battery against the photos before ordering.
How do I find the right adapter on this page?
Use the selector at the top: pick the platform on the other side of the pair and it takes you straight to the one adapter that joins them. Every combination in that list is one we actually make, so if it is there, it exists.
Can I use a Stanley FATMAX 18V (Old) battery on another brand’s tool?
Not with an adapter from us. Stanley FATMAX 18V (Old) works as the tool side only here — we make adapters that let other brands’ batteries run Stanley FATMAX 18V (Old) tools, not the reverse.
Can I charge a Stanley FATMAX 18V (Old) battery through the adapter?
No. The adapter carries current from the battery to the tool and does nothing else — there is no charging circuit inside it. Keep charging Stanley FATMAX 18V (Old) batteries on their usual Stanley charger.
Will an adapter damage my Stanley FATMAX 18V (Old) battery or my tool?
Used with undamaged, compatible equipment it is not expected to. Stanley FATMAX 18V (Old) batteries are lithium-ion with their own protection circuit built into the battery, and it keeps doing its job through the adapter. Stop when the tool noticeably slows rather than running the battery flat, and stop using the adapter if it becomes unusually hot or the contacts look damaged.
Does it work with third-party Stanley batteries?
Usually. What matters is the socket, not the badge: if the battery slides onto a Stanley FATMAX 18V (Old) tool and locks the way an original does, the adapter will take it. Aftermarket batteries do vary in moulding, so if yours looks unusual send us a photo and we will check before you order.