There's some kind of rust in the battery.
The battery on these cars are sealed batteries and if you are seeing rust and corrosion in the battery box and on the battery then the battery is leaking acid and the battery would need to be replaced. The cables, battery box and wires would have to be checked for acid damage and cleaned of all acid that leaked out. I recommend having the battery and surrounding area checked for needed repairs. After the battery and area is fixed then the charging system will need to be checked for overcharging the battery. I recommend to have a qualified mechanic check it out such as one from YourMechanic.
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