Made the same mistake. Even drone courses don't mention anything about how to store batteries.I received my new charger from AMZ, ISDT 608 AC, with click wheel and detailed color LCD screen.
Perhaps overkill, but it seemed well reviewed
Plusses to me are: I can see all the cell voltages at a once and don't have to do a lot of button pressing nor deal with a single line calculator screen user interface. I don't have to memorize or hunt for settings as it is a visual UI.
And, I can do storage charging!
What killed my batteries, is the default charger from Yuneec and lack of instructions, so I treated them like power tool batteries and just kept them charged up.
Looking forward to flying again, soon!
... now where is that first flight manual?