When files are copied from XQD/CFExpress/SD Card to internal SSD temperature of card, internal SSD, battery and case is increasing.
That is somehow normal process when doing file operations on SSDs or flash memory devices.
I already owned NextoDI NPS-10 XQD which has almost same behaviour, but the battery of this device is not that close to SSD like with Clouzen Tainer V2. Clouzen Tainer V2 is getting quite hot, as battery is very close to internal ssd I would like to know how safe this is.
You are right. Heat generated whenever power consumed. That is rule of physics. And understand your worry about it because battery seems close to the SSD. But if you unfasen TAINER and see the mechanics of TAINER carefully, you can see the battery never contact to the SSD but fully contact to the outer Aluminium case of the TAINER. See the internal of the Aluminium case. As below image shown, you can see there are slot holding the battery when assembled. Also, in oposite side of the battery is held by steel case an hang to the plastic body to make battery not attached to the SSD but strong contact to outer aluminium case. That is how TAINER make it safe.