It’s almost certainly the batteries, there are 2 on each side. I bought 100 of them for $7 on Amazon.
BTW to get the stacks off, use a spoon as they are tapered and the “string trick” doesn’t really work 
It’s almost certainly the batteries, there are 2 on each side. I bought 100 of them for $7 on Amazon.
BTW to get the stacks off, use a spoon as they are tapered and the “string trick” doesn’t really work