iPad battery draining and lagging after iOS update

Having trouble with battery drainage and constant lag if i have more than 2 apps open at once, it’s happened ever since my original charger died out due to over usage, im doing the same things but ever since i went from ios 18 to 26, my battery had been draining like heck, any ideas on how to fix it? (and no i dont play any games nor do i use big apps, i use my ipad for school purposes only)