Nintendo splash screen then no boot : entering RCM with NSL?

Hi, I’ve on my desk a Nintendo switch lite. I got it from a seller that told me he let the battery discharged completely and could not boot afterwards. I already went the charging with a little current for hours, then moved to the big block for some hours more. The unit was warm which would indicate that some activity (charging ? cpu ?) was happening.

Still, it wouldn’t boot. When I connect a charger, the Nintendo logo will be displayed shortly (for some seconds) then the screen will black out.

I wanted to get more info on the device using Hekate but I’m not sure it is possible on this console generation, plus I don’t know to make it boot to RCM. Any clue ?