Officials said on Wednesday they were hopeful the rover would survive the storm, which already covers a quarter of Mars and is expected to encircle the planet in another few days. It could be weeks, or even months, until the sky clears enough for sunlight to reach the surface and recharge Opportunity’s batteries through its solar panels.
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The rover’s batteries are likely so low that only a clock is still working, to wake the spacecraft for periodic power-level checks, according to officials. If the clock also goes offline, then the rover won’t know what time it is when it comes back on and could send back signals at any time.
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In 2007, a massive dust storm kept Opportunity silent for a few days. It jumped back into action after awakening from its deep self-protecting slumber.
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This time, the rover’s energy level is believed to be much lower. However, Martian summertime is approaching, which should keep temperatures up at night and prevent the batteries and other parts freezing. Besides electrical heaters, Opportunity is equipped with eight tiny plutonium-powered heaters.

https://www.theguardian.com/science/2018/jun/14/mars-storm-nasa-rover-opportunity