The saber saw battery won't charge.
You first check the charger itself has no output voltage. If not, there is a problem with the charger, if there is voltage, you have to check the battery, if it is a lithium battery. There's a protective plate inside the battery that's protected. You need to find a way to recharge.
If it's a water battery. Check the battery for water. There is water but it cannot be charged. The battery died. You run out of water, you have to add battery water.