Ta for the tip, I avoided that as I had all sorts on it and wasn't sure it would be preserved.Ever do a factory reset, set it back to the original install that it came from the factory?
That helps as far as the slowness goes, you get rid of all the crap left behind from stuff you've installed and removed over the years.
Battery life going? You can replace batteries as they do have a finite life and the more you use the tablet the faster the battery life goes.
Not defending Samsung, I think they're over priced and come with too much shit pre-installed so wouldn't get one, but a full reset is something that everyone should do on a regular basis just to get rid of the accumulated crap, imo.
I've replaced it now so will take a look from the perspective of a learning exercise.....Cheers