Cumulative faiure rate of Ni-Cds
Here is what you can expect of a 4 cell Ni-Cd pack in the way of failure rates.
Fairures Weeks
1.00% 123.1
2.00% 146.6
3.00% 162.5
4.00% 174.8
5.00% 185.1
6.00% 194.0
7.00% 201.9
8.00% 209.0
9.00% 215.5
10.00% 221.6
11.00% 227.2
12.00% 232.5
13.00% 237.6
14.00% 242.4
15.00% 246.9
16.00% 251.3
17.00% 255.5
18.00% 259.6
19.00% 263.5
20.00% 267.3
21.00% 271.0
22.00% 274.6
50.00% 354.9
Bottom line - half of your packs will have failed after 6.7 years
This is at an average temperature of 73 degrees F
Raise this to 90 degress F and 50% will have failed after 3.1 years with 1% failure in 1 year.