Any idea what karat 825 Chinese gold is?

Most likely you are seeing 925 instead of 825.

.925 is the purity of Sterling Silver, which is often plated with gold and sold as "vermeil". It is legally stamped with the purity of the majority metal, which in this case would be 92.5% silver, 7.5% copper and a trace amount of gold for electro-plating.

It could be a genuine quality mark. 18kt gold has a quality mark of 750. This is 18 divided by 24 (maximum gold purity), giving 0.750, which becomes 750. ) 0.750 means that 75% of your ring is genuine gold, and 25% is other stuff. 14kt gold is marked as 583 - interestingly, even though it is still called 14kt gold, most 14kt material is actually 585. This is sort of a "guarantee" that it's 14kt, because it might be a tiny bit more.

You have an 825. So if you do the math backwards, you get 19.8k. If you didn't follow the math, it was: 825 becomes 0.825, then the equation 0.825 x 24 = 19.8.

So, either your bracelet is a rather unusual 19.8k, which is either a really good deal on 19kt, or getting screwed out of a few bucks buying 20kt... or possibly, 825 has nothing to do with the karat of the gold. However, as even China tries to stick to international standards, it's probably a real quality mark, just a strange value. The "SI" part probably just refers to making sure that people know that International Units are being used - which adds credence to your having a piece of 19.8kt jewelry.

That's probably a safe bet as a good answer for you.