I had quite a collection of AA rechargeable batteries, enough to have 2 sets for my Inon strobes, and 2 sets for my Fisheye focus light. Although I kept matching sets of 4, I had all sorts of different brands, capacities, and ages of batteries accumulated over the years. Everready, Sanyo, Powerex, etc.
Here's what I assumed all along:
You are supposed to get about 1000 charges from a NiMH, and I recharge maybe 10 times a trip, 4 trips a year, so they ought to last at least 5 years.
A set of matched batteries would deteriorate at roughly the same rate.
Store the batteries charged, and charge again before each trip.
Then I started to unexpectedly run out of strobe power in the middle of dives. So I splurged and bought 2 Powerex MH-C9000 Charger Analyzers( http://www.thomasdistributing.com/maha-mh-...ery-charger.php ), and boy, did I learn a bunch. This device, which costs about $50, will break in, charge, discharge, condition, and/or analyze up to 4 AA or AAA batteries. Each battery is charged/analyzed independently and there is a bright LED readout to monitor the status of each battery. In the Break In or Refresh and Analyze modes, the capacity of each individual battery is measured and recorded, so you can know exactly what condition your batteries are in. You can even re-condition some batteries and improve performance.
Here's what I found out from analyzing my batteries and reading the very informative instructions:
1. Most of my batteries were at 2/3 or less capacity, probably as a result of improper maintenance and age. My 2500 MAH Sanyos were measuring 1700-1800
2. I had quite a few batteries that read much lower than others in the same set. Since the capacity of a device using a set of four batteries is limited to the capacity of the worst one, I was not getting nearly the performance out of sets that I should.
3. I was damaging my batteries by not charging them for months, and charging them together at a very high rate using the cheap chargers that came with the batteries. These chargers stop charging as soon as the first battery is charged, the others are not charged to capacity. They charge fast and hot, which is not the best for the batteries. Also, AA batteries need to be refreshed/recharged at least once a month while in storage to keep them in top form. An intelligent charger like the 9000 will charge at a rate that is the most efficient and least damaging to the battery.
4. Brand new batteries are no guarantee of reliable performance. I bought 8 Delkin 2900 MAH batteries from Thomas, ran them in the break-in mode on the c9000, and found out they were only holding about 1900 MAH. I sent them back, had them replaced with Powerex 2700's which tested at over 2600. Without this device you just buy and hope.
5. You lose 1% a day from a fully charged MiMH battery just sitting. And I would sometimes charge my batteries a week or two before a trip. So you might lose 15-20% before you get in the water. So now I top off all my batteries before the first dive.
I ended up just throwing away all but 8 of my old batteries, and buying 16 Powerex and 16 Sanyo 2700 MAH batteries, all of which tested at or near rated capacity. And I just got back from Hawaii, where for the first time in several trips I knew before I hit the water I would have enough strobe and modeling light power to get me through the dives I had planned.
The 9000's are pretty bulky, so I use them for charging and maintenance at home, and carry the light, cheap wall wart-type chargers for trips. Since I now know exactly the status of my batteries before I leave, the cheap chargers work fine for a week or two.
Hope this is helpful.
Mike
PS Two things to add;
First, the Sanyo 2700 MH batteries have proven to keep capacity over time better than the Powerex 2700's. The Sanyos are measuring 2400 and the Powerex are measuring about 2200.
Second, I'm told that a severe drop to high capacity NIMH batteries can ruin them. If you drop one on a hard surface, be sure to test it before trusting it.
Bigger is better.
