Battery increasing in capacity over time?

Someone who is smarter than me about lead acid batteries please explain why it appears that battery capacity is increasing every year…

For the past few years, I have been testing some batteries with a West Mountain Radio CBA IV Battery Analyzer (7.5A down to 8.5V). In both of our 2014-1 and 2014-2 batteries, the capacity appears to have increased. I’m not too certain why the 2014-1 test appears to be a bit “choppy” this year, but it probably had to do with me bumping the wires at one point (is it really that sensitive?). I don’t really want to torture the batteries in another retest to find out. Do I have magic batteries or is there something goofy happening with my battery analyzer/test setup?

Also, sorry about the chart legend being out of order…not quite sure how to fix that without importing the data into Excel (which I can do, but I’m pretty lazy)

**Global Warming?
Have you been keeping the batteries at a consistent temperature, like is the shop warmer than it was for the test the previous year etc.

Temperature greatly effects a SLA’s capacity/output energy.

As temperature increases the capacity of the battery increases

I can’t really say (mostly because I don’t know) if it was really any warmer. During the first couple of tests, they were in our shop and the most recent ones were on my workbench in my apartment. The shop was probably a bit colder, but trying to remember the room temperature 2 years ago…well…who knows?

While we haven’t kept sufficiently detailed records to clearly prove or disprove this, we do label our batteries with the year we procured them, and there is a definite trend downward as time passes. If you have a recipe that improves batteries for a year or two, please share - we’d love to see if we can incorporate it into our usage profiles!

Edit: That said, we have rarely used our batteries below 20C/68F, except in preparation for the 2014 competition (Aerial Assist), in which we practiced mostly in an outdoor parking lot.

Although testing conditions will influence the results, the three curves are about identical until you get to the knee at 10.5 volts. Beyond that is somewhat unimportant. Odd but not a miracle.

I’ve been really mostly concerned about dead cells, but the capacity thing confused me.

A quick question:
Are you using the same chargers that you were using 2 years ago?

Here is a neat site that has a lot of articles on batteries, battery management and pros/cons vs. types:

Anecdotally, I have heard with specific types that there are different techniques you can do to increase a batteries capacity.
During the minibot effort in 2011, I heard many rumors of different tricks that would eek out slightly different performance curves. Slight changes to charging rates and voltages.

During my solarcar days, I remember hearing about a team doing controlled battery cycling using a specially designed oven to increase a batteries useable capacity. While controversial, I will say that particular team was able to run much longer in cloudy weather than all the other teams so I have to believe there was something to the effort they were doing.

Yes, all batteries are charged with the Schumacher SC-600A chargers using the 2A setting prior to testing (though 6A is normally used at competition). There may have been various amounts of rest between charge and testing, but I wouldn’t expect the capacity to change too much.