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rv7charlie

Well Known Member
Read the reviews

Seems to be a consistent theme of less-than-expected reserve capacity.
 
RONSIM said:
Seems to be a consistent theme of less-than-expected reserve capacity.
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That's the nature of marketing strategies for lithium starting batteries. To play devil's advocate, it kinda makes sense to the marketers, since auto/offroad/personal watercraft aren't really expected to operate continuously after an alternator failure. We just need to have a clear understanding of the difference between power and energy, when we look at this new tech.

If you have an electrically dependent airplane, making an electrical power source change could be just as critical as making a chemical power source change. :)

Charlie
 
These batteries pretty clearly say "21ah lead acid equivalent" and then 76.8 watt hours.

76.8W hours is only 6.4 amp-hours at 12V. Less at higher voltages a LiFePO4 battery likes. So it's about 1/3 the capacity of the standard PC680.

Lead acid weighs about 1 lb per amp hour (for a 12V battery).

LiFePO4 weighs about 0.4 lbs per amp-hour. There's no magic here- of the LiFePo4 battery doesn't weigh 5 lbs or more, it has significantly less capacity than a 16 lb lead acid battery.
 
Need to see if the bettery has a battery management system built in like EarthX.
 
I now have EarthX in both my aircraft. I have been using another Lithium battery brand in my RV8 for 2 years.

HUGE DIFFERENCE when I push that start button!

Previous lithium brand during start would stop on first blade pass..... then start turning again for the actual prop rotation.

EarthX starts and surprises you! I could taxi the plane with just the starter button! (Not trying to exaggerate, it is truly a HUGE difference)

I hate hooking up trickle chargers. This is one of the big plus factors for me. EarthX does not discharge like standard batteries. Having 2 aircraft, one is always sitting and waiting to be flown. No battery low issues to worry about with Lithium.

I love the internal balance charge function too (other brands require an external balance charger). If your battery is not balanced, it will trick your voltage regulator (I speak from experience). I also feel much better flying with the protections that EarthX provides in their built-in protections.

This is the battery I took out and the EarthX I replaced it with. I'm very happy;)

 
Difference between starting and deep cycle service

I don't post much here because as a wannabe builder I don't feel I have much to contribute. However I have been studying lithium iron batteries for deep cycle service in boats, and when you start talking about reserve capacity you begin to get into that realm.

There are thousands of posts on this technology on cruisersforum.com, and anyone interested in these kinds of cells would do well to read those threads. Some of what you read there will run counter to the notion that a drop-in 12v replacement battery can be constructed from LiFe cells.

The reason that marketers get away (legitimately, IMHO) in talking about "lead acid equivalent" capacity is because in deep cycle service you really don't want to discharge a lead acid battery below 50% because it seriously degrades battery life. This is true even with deep cycle cells which have a different plate design than starting cells. Furthermore, you can't rapidly charge past 85% of capacity because you boil off electrolyte. So you realistically wind up with 35% of stated capacity as usable. Worse, if you don't routinely recharge lead acid back to 100%, you suffer sulfation, which degrades capacity. LiFe doesn't suffer from either of these problems--you can discharge them further, and recharge them at higher rates for longer than with lead acid. My next set of (boat) house batteries will likely be LiFe.

Now none of this matters a whit in the aircraft alternator failure scenario. If you need to you're going to use that battery until it's depleted, you don't care how much it's been degraded, and you don't care how long it takes to recharge.

This technology is as different from lead acid as aluminum airframe construction is from composite, and it's critical to separate the hype from the reality.

Doug
 
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