Testing is always good, but John has a very reasonable suspicion the
problem was due to cold soaking the batteries. LFP's really don't like
the cold, and can even be damaged if charged below freezing. Maybe he
had a temporary loss of capacity that wouldn't show up under room temp
testing.




On 5/30/20 8:50 AM, SF wrote:
One of my early K2's experienced a cell failure which dropped that battery's voltage output and lowered it's capacity. I run two batteries in parallel and had an experience like yours. Individual testing of each found the bad battery. Replacement is the only fix for this.

Battery testing can be done pretty easily and low tech. Using a voltmeter and 12V side marker lights from your local tractor supply. , 2-4 of the side marker lights should approximate your gliders normal electrical load. Plug them into the battery then check and record the voltage every half hour until it drops to 11.5V.

You can measure amperage with most multi-meters, just be careful to switch the leads back to voltage measurement. The cheap meters are not fused. Had a guy blow one up checking 480V with an un-fused meter set to measure current. It can cause serious injury, so exercise caution. The batteries we use in sailplanes can deliver enough energy to melt things if shorted out, so respect that potential when dealing with them. We had to evacuate a 300,000 SQFT manufacturing facility once because a technician shorted out a single lithium Ion battery cell in his test stand, The smoke from off-gassing was impressive.

SF