I've never paid very much attention to acceptance rates, because my charging sources are relatively meager (solar mostly, with a bit of smallish alternator). Out of curiosity I just went and looked up the Lifeline acceptance rate (that's what I have). If I understand it correctly, they recommend .2C minimum (20 amps for 100ah battery) and 5C maximum (500a for 100ah battery).
In comparison, 13% would be....13amps for 100ah battery. I know AGM have a higher acceptance rate, but that does seem really low, doesn't it?
OTOH, if your batteries are 8 years old (and assuming you use them regularly), you can't say you haven't done well with them.
Okay, I got more curious and looked up Trojan's flooded cell recommendation. They say 10-13% of C20 (the 20 is small). Does that mean something different than "C" as Lifeline uses it. What is the little 20 about? In comparison, they list their (Trojan) AGM as 20% of C20. So are they expressing it differently than Lifeline and it's not really so low? Or is that just how flooded cells are?
Next, I Googled. Oh, C20 is the 20 hour rating. So I guess it is apples to apples with Lifeline and that's why the AGM acceptance rating is a big thing (for those like you who have large charging ability).
So I guess it goes back to your 8 years is none too shabby; maybe pretend you didn't read it?
I guess if I get a trawler with a big alternator I, too, might have to start concerning myself with acceptance rate vs. my slow but steady "tortoise" solar panels