I have a X62 (x61 with a custom mobo with updated everything) sitting in a box now. My build is 6(?) years old and still works like a champ. But the battery is

I have a X62 (x61 with a custom mobo with updated everything) sitting in a box now. My build is 6(?) years old and still works like a champ. But the battery is the main reason it’s in a box. You have to use it like a desktop and keep it plugged in within a hour or two which really defeats the purpose of a laptop…