Is my digital scale broken or is it the battery ?

Is my digital scale broken or is it the battery ?

It was working fine when I weighed myself this morning but I weighed myself again and I weighed 10+ pounds more

Then I turned it off and on and when I stepped on it, it would weigh 50 lbs and goes back down to zero even when I was still on it

I thought it was broken so I asked my mom she said it could probably be the batteries. So should I replace it or should I replace the battery?