I purchased two 630F 2.5V(max) super caps recently. They do not perform the way I expected. I charged my caps at about 1A until they reached about 2.4VDC, so I would not over charge them. I left them overnight, when I check the voltage in the morning they were both at 1.3VDC. I did not expect this loss.
So, I decided to test this in the morning and I charged them again to 2.4V. After charging I placed a voltage meter on one cap, and the voltage starting bleeding off and in about 15 minutes it was down to 2V. This was like a bleeder resistor was on the cap. I had nothing but the meter on the cap and only for a few seconds then removed.
The point is expect this lower steady state voltage after charging of about HALF of the maximum rating. I paid $20 for each cap plus shipping. Also, the 630F capacity is only about 0.6 Watt-Hours, so pretty low capacity.
Super caps should be used with some care, but there are NOT a battery.