In my experience, cheap is just fine. I have a couple of slightly higher capacity batteries and I only use them now. They are very nice and I don't remember where I got them, but not ebay, which I am permanently boycotting. Just google and you will find similar deals.

I use a cheap charger I bought from ebay a couple of years ago.

I don't have spares for my N810.

It appears to me that when you buy cheap Hong Kong batteries, you are getting good quality batteries, as a rule. No one has reported their tablet damaged by a battery here, ever