Finally coverage on supercaps10 Aug 2018 17:53
https://www.phonearena.com/news/Galaxy-Note-9-S-Pen-battery-super-capacitor_id107622
Supercapacitors do not degrade as quickly as batteries do. Lithium batteries – the kind used in practically all phones, tablets, and laptops nowadays – gradually lose capacity as they age due to the chemical processes going on inside of them. Every charge-discharge cycle shortens its lifespan. It is not uncommon to observe a noticeable drop in a smartphone's battery life after a couple of years of use. A supercapacitor, on the other hand, can last a decade if it is used properly, which is great as I'm sure an S Pen battery replacement service wouldn't have been cheap or easy to perform.
A supercapacitor won't mind staying fully charged all day. Another way of killing a lithium battery faster is to leave it empty or to keep it at full charge for a long time. If treated like this, they tend to swell and cause all sorts of trouble. In contrast, having a supercapacitor fully charged for months will have very little (if any) impact on its longevity – perfect when a Note 9 S Pen would be fully charged 99% of the time.
Supercapacitors charge rapidly. Lithium batteries are tricky to charge. They require specialized circuitry and go through several charging stages before they reach a fully charged state. Supercapacitors can be charged literally tens and hundreds of times faster, which is probably why the Note 9's S Pen charges fully in 40 seconds.