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Old May 12th 18, 12:52 AM posted to rec.aviation.soaring
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Default A Simple Question About LiFePO4 Batteries

On Saturday, May 12, 2018 at 7:00:52 AM UTC+10, wrote:
I don't usually drain them. I switch to the backup if I'm on a long flight or it's cold. Rarely does the main batt go low enough to get the "low battery" warning blinking (11.2v). They don't cost that much more than the standard-size SLA battery. And they probably last 3 years on average, IIRC. I haven't done any testing nor do I write a date on them when installed. I just usually replace them when I have to start going to the backup on long flights.

So I'm surprised that a relatively new battery (2 seasons?) hasn't performed that well in two flights this spring. The last time, I decided to stay with SLA because it had worked well enough in the past and was a lot cheaper. But now that I'm facing replacement again so soon, I'm reconsidering.

Chip Bearden


You may well be discharging your battery more deeply than you think, hence the short life. 11.2v open circuit for a SLA is well below fully discharged at around 11.7 to 11.8V open circuit, but your meter is probably showing you the voltage with a load on so you really don't know how deeply discharged the battery is. If you want to check the actual approximate state of charge, put a multimeter on the battery after it is disconnected from all loads.. The table in the following article shows an approximation of state of charge based on open circuit voltage (from 100% @ 12.7+V to 0% at 11.8V) for various types of LA batteries.