iPad Pro M1 battery draining on standby

I have been using iPad Pro m1-11 past 6 months. Last 2 months, I did not get time to use it regularly. So it was used for less than an hour daily. It was on standby most of the time. I did charge it when it came down to 30% or 40% to 80%.

So, here's the thing now I am using the iPad daily for 2-3 hours.

I am facing an issue with the battery. Suppose the iPad is charged 100%, then I start using it, and the battery goes down regularly. So, when it comes down to 60 or 70%, I put the iPad on rest for 10 to 20 mins, then I open it again and see the battery is on 40% or less within 10-20 mins. (I close all the apps, wifi-bt are turned off, background refresh is off, location is off, cloud sycing is off before stop using the iPad.)

I did a factory reset a couple of times to fix it. Nothing happened. I bought the iPad brand new. It's charged only 50 times, and battery health is 100%.

What might be the issues here?

Is anyone facing the same issue?

Please, help me.