Whether the battery is unsafe or not is almost irelevant. At 3 years old the rechargeable battery very likely has severely reduced performance and no-name brands like Vokul are manufactured as cheaply as possible: aftersales care is typically non-existent so it's not at all unusual to find that they don't even last the one year warranty. On top of that you'll probably find that the motors could be nearly worn out: many users are overweight salad-dodgers and put a huge load on those machines.

At $150 (I'll assume USD) the price is ridiculously high given that far better new ones with a full warranty with much improved battery performance and safety are available for not a huge amount more. If it was a third of that price it might be worth a risky gamble. At half that price it might have been worth a risk if it was a bit less than a year old with some remaining usable warranty.

Leave it. Overpriced rubbish.