Or they use smart cards or USB sticks introduced directly into the unit by the technician. A part of maintenance is also ensuring that the unit makes no suspicious noises or gives of excessive amounts of heat.
Some lithium storage systems have an internal cooling circuit using a circulation pump, where the bearings can start knocking. The resulting hum can be annoying and spread as an unpleasant vibration to the entire building via the wall suspension. (HS)
Look at this, too:
Storage advice: Check the plugs of the lithium battery
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