I totally disagree. I have a used 510 batt that was given to me when I bought my 510s. That 1 batt lasts me 4.5-5.5hrs. Lasts my wife 8-9hrs. I mistakenly interrupted the 1st chg on my 2 new batts, and can't get more than 1.5hrs out of them to save my soul.
The 1st chrg is ultra important for batt. length. Proper chrg on a new batt is:
chrg for 8hrs.
Vape for 20 mins.
chrg for 1 additional hr.
After that, chrg 4-5hrs for optimum performance.
Never plug chgr in with a batt screwed in.
I am living with proof that this method works. I get the theory Ni-cad batts have no memory. IMHO, that's simply not true. And as I say, I'm living with the proof.
I'm a noob, but was taught this by my VERY non-noob supplier. So there you go. Pick one.