Battery storage help

[Rustypeb]

Hey all, hope your all well?
Last week I brought 2 more set of 2s lipos second hand again but from my local shop and got both for the price of 1 new.
Now my main question I have been using the storage setting on my charger for storing my battery's but he said just charge/discharge to 7.5v need to check what voltage my charger takes it too on storage mode. But what would you say is best?
also my older batteries are 5100mah the newer one are 5800mah he said to set the charger too charge at 5800 and it will be fine for both is this safe?
Thanks
Russell