"Li-ion". A way to restore NP-FM50 by booslting charge curre

[Stason]

Hello guys !
Please, help me with the following situation, any advice is appreciated !
Three month ago I bought an extra NP-FM50 original Sony battery for my F717. New, it has given me 240 minutes after full in-camera charge, and I was so happy. But a couple weeks ago it suddenly gives me 150 min. max. I did reset the camera, discharged and charged again a few times..., nothing helped.
Than, after reading reviews of my folks at this great site, I purchased an Ambico V-0916 - it still charges that battery up to ~200 minutes charge, no more.
Than I replaced my Ambico V-0916 to a "Sima SPM-13N" as I was hoping to restore the battery by pressing he "booster" button on the Sima SPM-13N. But I had no slightest idea that such a magic button is only in the older version of this charger - the "Sima SPM-13" (with no N at the end).. After a few charges by Sima SPM-13N the battery gives me 215 minutes. If I need to return my Sima SPM-13N, I must do it fast, within 8 days.

So, the question to you, folks : do I have to get a Sima SPM-13 with booster button? Will it help ? I would like to ask those of you, guys , who have a Sima SPM-13: does it really help in situations like mine ?
Or, maybe that is just a dying battery and nothing to do with charger? But than's so strage.... this battery is really new, and it is an original, Sony OEM.......

Please guys, give me any info/advice/ share your experience. I need to decide whether return my charger and get the one with the "booster".

Thanks a LOT !!

Stan.