How do stats on Soul Ripper work ?

Trying to understand some of the stats on Soul Ripper before buying for build. Specifically these two

Consumes # of # charges on use - this one is fairly obvious - it will use # number of charges. As I understand it though the flask has to have 50 souls before it can be triggered ?

If the number is higher (say 70 or 100+) does the flask wait till it is full (at the 70 or 100 mark) or will it fire at 50 and then use the left over for the next set of charges to build up (souls in the bank so to speak) ?

The other stats not clear about is # to maximum charges. Is this number (negative or positive) in addition to the charges used number or a part of it (so 50 charges becomes 75 is it is +25 to maximum charges or 48 if the number is negative) ?

Here's some on trade for reference - https://www.pathofexile.com/trade/search/Standard/LBwpzGHn

Soul Ripper always uses its maximum charges as far as I understand it.

You would probably want it to have as many maximum charges as you can store vaal skills, or possibly slightly less than that if you intend to refill them more gradually (e.g. because they have several stored uses and you would rather not wait for full charges and just refill your souls after 1-2 uses of the vaal skill).

The flask does not activate on its own unless you add an enchantment to it that uses the flask when a certain condition is reached (e.g. reaching maximum charges).

+# to maximum charges is additive with the base 60 maximum charges that a quartz flask has by default.