Using iPad as a 24/7 kiosk on continuous charge

We are using iPads as a feedback hub in a facility. Therefore it is required to be connected to power 24/7. It is contained in a secure iPad enclosure, with settings set to a single app where the consumer/public enters information. The accessibility settings do not allow access to gestures, not are the power and home buttons accessible.

The primary issue concerns the long term effects of the iPad remaining on charge? The iPads have been used for 2 years and now seem to randomly shut down, even when still on power. They can be woken up by turning power on and off again, however this requires the iPad to be removed from the secure enclosure.

I would like to hear from anyone else using an iPad as a 24/7 accessible kiosk and how the issue of remaining on power is managed.