some batteries will have a small PCB were the wires solder to, it is the protection, most common is over charge, discharge and current protection, because over discharge will reduce the life of the battery and the 2 others have a fairly big chance of making it catch on fire, not all batteries have them because it cost money to implement and a fair number of battery using appliance have those integrated, from the photo i can't see if the wires are soldered directly to the tabs of the battery or a protection board, and i have no idea if the board you bought has any of those protections so it is why i warned you, i am guessing the board should at least have a charge IC so not risks of overcharge, and being a keyboard there is a good chance something would burn before the battery in case of over-current (those type of batteries can supply multiple amps i feel like the resistance of the traces should be enough to prevent that) leaving over-discharge as likely your main worry, not too bad but i also made assumptions that may not hold true