Well, I have some non-scientific data to share with my charge/discharge cycles of the five batteries that I use.
Unfortunately I don't have a multi-meter, so couldn't use any baseline voltages for comparison.
However, here is some useful information, or at least I think it is.
1. Batteries: 4 Minolta NP-400, and 1 Sigma BP-21 (All the same of course).
2. Test: Discharge and charge batteries 3 times.
3. Log the discharge time of fully charged battery on Sigma SD-14 "looping slideshow", with 2-second intervals, mode.
Oldest battery Minolta NP-400 about 4 years old, and approximately 35 discharge/charge cycles over lifetime:
Discharge time on slideshow: 1
2 minutes
Battery Minolta NP-400 about 4 years old, and approximately 30 discharge/charge cycles over lifetime:
Discharge time on slideshow:
28 minutes
Battery Minolta NP-400 about 18 months old, and approximately 15 discharge/charge cycles over lifetime:
Discharge time on slideshow:
2 hours, 40 minutes
Battery Minolta NP-400 about 18 months old, and approximately 10 discharge/charge cycles over lifetime:
Discharge time on slideshow:
3 hours, 10 minutes
Battery Sigma BP-21 about 2 months old, and approximately 10 discharge/charge cycles over lifetime:
Discharge time on slideshow:
4 hours, 36 minutes
Conclusion: Obviously pretty much what I would suspect -
1. As the battery ages, the ability to hold a full charge decreases.
2. The higher numbers of charge/recharge cycles possibly reduces ability to hold a full charge.
3. Surprised with the high degree of degradation of the older batteries that have about 30-35 cycles. I thought they
would do better, since they are advertised as capable of "hundreds of cycles".
What I will do:
1. I will retire the two oldest batteries to the recycle bin.
2. I will continue to keep track of the remaining three batteries, so that I know when to retire batteries and purchase new.