The best entertainment is watching an entertained baby. That's a fact.
We only have a single toy that's battery operated. It comes out when all else fails, and only when all else fails. To be clear, we haven't done this for a scientific reason, but only for our own sanity. There are limits on the sacrifices I'm willing to make for my child, I guess, and battery-operated toys are a bridge too far for me.
We love our Lovevery Play Gym. You can also do a subscription where they send you age appropriate toys at various intervals, or you can make one-time purchases. In the early days, their playset was perfect for our baby. We also bought a second, smaller playmat so our daughter could have a comfortable spot wherever we went.
We've also had great success with this Giraffe sucker, this crinkly paper, these blocks, and these cold chew toys for teething babies (it comes with a holder so baby can suck on a chilled toy without having to hold onto any cold parts).
Our baby's favorite toy is not a baby toy at all, but rather an empty, cleaned Planter's Cashew can. It's colorful, grabbable, rollable, and loud. In other words, the perfectly engineered toy for a baby.