What do these indicate ?

Top left: Dian4yuan2 zhi3shi4 deng1 - Power supply Indicator

Middle: Chong1 bao1 zhi3shi4 deng1 - Filling indicator

Bottom left: Chong1 yuan2 zhi3shi4 deng1 - Charging indicator

My Mandarin isn't good enough to tell what the middle one really means, it's just the literal translation. I've included the pinyin in case that helps - hopefully someone else can clarify.

Thank you, Prometheus. 

"Filling"...  hmmm... Could the green at middle mean something like 'tuned' or 'receiving' or 'station present' or 'active channel' or 'squelch open' or 'unsquelched' ?

充饱 is usually used in the context of a battery being fully charged. So I guess this means that, when the green light comes on, the charging process is complete.

Knowing what is the function of the device would help.

It is an AM aviation band radio receiver :

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It’s battery operated (as I suspected), so the green light indicates that the battery is fully charged.

Thank you, Markus.  Perhaps  'end of charging has been reached - the charger can be disconnected now' 

As  'battery is fully charged'  would imply the indicator could come on even while not connected to the charger or the receiver not even turned on,  as long as the battery is fully charged.  Just trying to read between lines...

At least fully clears the doubt that is not related to tuning.