On Saturday, February 18, 2017 at 6:23:54 AM UTC-8, SF wrote:
Based on advice offered in this post, I left the old K2 batteries on float charge for several weeks to "equalize" the cells and attempt to revive their performance. (charged in parallel). I tested them yesterday with the two batteries in parallel powering a 2.3A load of side marker lights. I placed an amp meter on each battery capable of detecting reverse current (one battery charging the other battery) These batteries have very different discharge curves. At the start of the test, battery 2 was shouldering 1.7A of the load. At the end of the test battery 1 was shouldering 2.06A of the load. At no point in the test was there any reverse current or evidence of on battery charging the other battery. Leaving the battery on float did improve the combined Ah from 11.22 to 13.9Ah, better, but not back to acceptable for (2) 9 Ah batteries in parallel.

Conclusions:
-no observed problems with operating batteries in parallel on a common 12V bus, no evidence of one battery charging another found.
-These batteries have an observed life span of 5-6 years regardless of the advertised 2000 cycle lifespan.
-LiFePo4 batteries are still the way to go.
-Test your batteries at the beginning of each season to verify that there is sufficient capacity actually present to power your glider's load.

Disclaimer: This is based on a data set of 2. your individual results may vary significantly.

Enough of this, lets start flying again, instead of talking about flying.

SF

Did you run only one discharge-recharge cycle? Some BMS cell balancing schemes seem to require a few deep discharge/full recharge cycles to properly equalize the cells.

If you decide to dispose of these batteries, I suggest cutting open the case and measuring the voltage on individual cells. This would tell us if cell balance, or basic loss of capacity is at fault. Always good to learn something.