Test results LiFePO4 glider batteries after 6 years

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

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.

SF: Yes, as Jon says, one cycle might not be enough. My batteries came back after successive long charge cycles with discharge in between as noted in my 2/29 post above. You may be tired of screwing with it, but you did get a substantial improvement with one long charge; it'd be interesting to see what a second or third would do.

It's a lousy state of affairs that these batteries can require such babying..

I'm game, I'll repeat the charge discharge process a few times and report back.

SF

I have three K2 9.6 AH Lifepo4 batteries. I used a West Mountain Radio battery tester. Two of the batteries showed 8.7 and 8.5 AH for a full discharge (test cutoff at 10 volts) at 2.5 amp discharge rate. That seemed reasonable; however, the last battery showed 7 AH and that seemed low. These batteries are all two years old. I spoke with K2 Battery technical service and they suggested that the lower capacity battery could be improved by several complete discharge and recharge cycles. I did three complete discharge and recharge cycles on that battery and it improved to 8.83 AH. So it does appear that that strategy does indeed improve their capacity. I did the same exercise on the other two batteries and they improved slightly to 8.9 and 8.7.

David
ASG29E BV

Sounds like this chemistry has a memory, sorta like NiCad and to a lesser extent NiMh. The LiFe does not have anywhere near as much the same issue it seems, but has it to a point.
I guess that means typically the batteries need to do a full discharge then charge a few times during a season just to keep it up.

Good info here though, thanks for posting.

On Sunday, February 19, 2017 at 3:22:29 PM UTC-5, Charlie M. (UH & 002 owner/pilot) wrote:
Sounds like this chemistry has a memory...

No. This is about cell balancing.

If they have a built in balance board, how is this balancing?

On Sunday, February 19, 2017 at 3:28:49 PM UTC-8, Charlie M. (UH & 002 owner/pilot) wrote:
If they have a built in balance board, how is this balancing?

The balancing mechanism depends on charge/discharge cycles to work. More $ophi$ticated balancing schemes balance even with no load/charge.

On Sunday, January 29, 2017 at 1:41:07 PM UTC-6, SF wrote:
I started using K2 LiFeP04 batteries in my glider in 2010. I have had excellent results with these batteries. The electronics, especially the radio, enjoy staying above 12V, and I've never run out of power inflight with them.

This winter after taking some of the instruments out to have them calibrated & upgraded, I took one of these batteries with me to the shop to power everything up to see if all the magic smoke remained in the equipment after it was reinstalled. Imagine my surprise when nothing came on, and I found the battery at 10.5 volts.

This battery was charged after its last usage 1-1/2 months ago and left in a cabinet. Since these batteries are not supposed to self discharge that fast I decided to charge, and test them using two batteries in parallel on a 2.04A load. My six year old 9.6AH K2's were down to 5.4 Ah each, 10.8 Ah total.

I purchased two new Stark Power SP-12V9-EP LiFeP04 batteries and wired them in parallel on the same 2.04A load, and got 8.67 Ah each, 17.34 Ah total..

The tests were run until the voltage under load dropped to 11.5 V, not the 10.5V level where the battery management board turns off the output. There are probably some additional Ah's left in there after 11.5 V but not much, these batteries drop off pretty fast after 12.5V. The stark batteries are listed at 9Ah each.

The LiFePO4 batteries are advertised as having a cycle life of 2,000 cycles. Over the six years they were in use, I probably put less than 400 cycles on these. So obviously they also degrade with age and not just the number of charge/discharge cycles.

I still recommend these over the old sealed lead acid batteries. I also advocate annual testing to see if they still have the capacity you need, rather than waiting until they surprise you in flight.

SF

Richard just checked my 15 Amp and 12 Amp LifePo4 batteries purchased in 2013 from Bioenno, both are at 13.30 Volts waiting for the season to start. See you in Nephi