Slow charging after 90% happening sometimes?

[anon(10181084)]

So I've had this issue before (a few months ago) although starting at lower percentages like 83%. Basically it just starts to at a certain percentage dramatically drop the charge current to unusable levels. Expected to be greeted with a fully charged tablet after lunch today and I found it with 90% charge (not enough) with charging current effectively being a super low trickle charge (this is NOT normal behavior). I've also had issues with the charge going up to 95%, sitting for a while there and then immediately jumping to 100%. Another issue is that, even though I try to keep my battery from being discharged too deeply, it sometimes starts dropping more rapidly at 25-ish percent and before I am done with my tasks and ready to plug it in, it has already dropped down quite a bit more. This is mainly a problem when I use lots of external peripherals that do take some power while doing intensive stuff on the tablet (current draw usually 2800-3400mA, sometimes up to 3950mA in extreme cases). It's been working just fine for the most part until now aside from two occasions where the screen started flickering at 69% and 21%. I'm not sure, but the fact that until mid last year I didn't know full discharging was bad possibly already set the fate of this battery. Is there any way to recondition this battery a little as it seems to have 9% capacity (according to Accubattery last time I checked the health meter), or at the very least make sure this stupid charging current issue that happens sometimes. The tablet in question is an SM-T825 Galaxy Tab S3 LTE, purchased in July 2017 if that matters. Cycle count is 287, battery still works decently but has the aforementioned issues intermittently.

Edit/Update: just checked and it is at 100%. This behavior is freaking strange.

 

[Rukbat]

Sounds like a defective battery. (It could be a dendrite.)

Fast charging to 75% or 80%, then dropping to regular charge for the remaining charge, is normal. Dropping from fast charge to almost nothing isn't. (The battery is 6000mAh, so as long as you keep the drain down to 4000mA or less, you should have no problem. But draining that much for more than one hour will bring the battery low enough to destroy it. [Energy conversion isn't 100% efficient. You can't actually get 6000 mA for one hour from a 6000mAh battery.])

 

[anon(10181084)]

Yeah I know. And I know for a facf this tablet has overcurrent protection on the USB-C port which I am of course not tripping (I take care of my tech after all). Based on your experience, if I charge from 25-35% to 85-100 once or in some cases twice a day, how long can I expect this to last me before needing a battery replacement?