I've replaced batteries in many Android devices over the years - pulled them just to restart a stuck device, etc. Never lost a byte of data. The only thing you can lose is data you're working on that you don't save before replacing the battery, the same as if you turn the phone off before saving. Once something is saved, it's in "non-volatile" storage, meaning that it doesn't leave unless you delete it or flash a new ROM or something else that's supposed to delete data. (Of course if you damage the tablet [and doing your own battery replacement on a tablet always leaves that possibility], all your data can be gone [depending on what you damage].)
So, as belodion said, it can't hurt. (You should always have everything backed up anyway - what it you dropped the tablet and someone stepped on it hard enough to damage the motherboard? The data would go with it.) But see
Backing up an Android Device to back up
everything. (There's no reason to not have at least one backup - there are so many free cloud accounts. I currently maintain 3 - 2 cloud accounts and one backup on a PC.)