And the name of the mower is .................

As long as you can make and keep good connections between the batteries there is no reason it shouldn't work. Depending on the size or capacity of the batteries you may find they will run down faster than with the battery pack recommended for the mower.

You are seeing the unadvertised downside of rechargeable devices. They are convenient but the cost of battery replacement means many people just buy a new device when the battery needs a charge every 10 minutes.

A dead rechargeable mower should be inexpensive, almost to the point of free unless it is in virtually new condition. Remember rechargeable mowers will not be powerful mowers. If it was my money I would spend it on a new corded mower.