New battery arrived today - now the ispindel floats at 23.2 degrees in plain water with no extra weights - happy days!I had the same problem. First battery was a copy and only weighed 29g was a nightmare to get the angle lower than 70 degrees. Replacement ordered and quoted at 47g, just waiting for it to arrive.
Next step more detailed calibration - or do I take my chances and use as is ?!