Cause unknown decreased charging current

I have made a constant current and constant voltage batteries charger. The constant current is 200 mA.

When the deteriorated 1000 mAh Evolta batteries were discharged, they could discharge nearly 800 mA as follows in the next chart.

The actual current has to be scaled down 2/3. I missed the scaling.

I have been charging another deteriorated 1000 mAh NiCd GP batteries. I have found that 2SK1290 gate voltage is 3.16V lower than 3.37V as before. I don't know why the gate voltage has dropped.

Ref.
http://enokie.blog.fc2.com/blog-entry-1454.html