Do Light stones and Heat stones run out of power?
We see Onu-Matoran mining for them
Are they doing this because they need large quantities of them?
Are they doing this because they slowly fade and need replacing?
If so can you charge a Light/Heat stone back up?
Are headstones infinite energy?
Id like to think that they fade over time and need to be recharged by being exposed to something like energized Protodermis or something, otherwise they can be used as infinite energy.
The most likely reason for new lightstones/heatstones is that they might get broken over the 1000 years, we know the Matoran smashed all the lightstones in Mahri Nui in Prisoners of the Pit to avoid detection by gaint venom eel, so if a lightstone breaks it stops functioning.
Furthermore, lightstones and heatstones draw their energy from the central six great lightstones in Karda Nui, which in turn draw power from the GSR power source, which is designed to make energy infinitely. So yes, they do have infinite energy as long as the GSR functions. If the great lightstones loose their light, so do all other lightstones and heatstones.
Apparently if a certain area of MU has its own independent power source such as Metru Nui, it can also function to power up lightstones:
4. Are lightstones powered through Karda Nui?
4) And through Metru Nui as well