for using battery dashcam, driver could diy adding tint film wrapping the dashcam casing, juz don block ventilation holes.

doing this prevent plastic casing directly absorbing heat and pass on to battery

better still, first layer wrap with aluminium foil (kitchen usage cheap foil) + outer another layer of black tint film.

if using mr.diy black tint actually no big help as that mostly color dyed film only.