I posted the following on the Purple Board but thought I would also post here for those that may not follow that forum. This is just my personal experience and not an attempt to bash EarthX. Overall, they are a good company that continues to support home builders.

I finished building my Zenith CH601 XLB eight years ago. I chose EarthX for my plane due to weight. I have a heavy engine (Lyc. O-235-C1) and wanted to do everything possible to reduce weight. Since my first flight in 2016 I have gone thru four or five EarthX ETX 680 batteries in 600 hours of flying.

Note that I have an electrically dependent engine and so my comments are geared towards this condition. I need an electrical power or the fan stops.

Initially, I really liked the battery and the fact that it had "self-monitoring" capability. After living with these batteries I have taken on a new perspective.

First off, most of the replacement batteries have been because I left something on in the plane and ran it down. And this was the first misunderstanding I had about these batteries.

I was under the mistaken impression that they would shut themselves down before they permanently damaged themselves. Not the case. If you leave a switch on, the chance of being able to fully restore the battery is non-existent in my experience.

You may be able to get it to take a charge, but the reliability of the battery afterward is suspect. In my case I could charge them and they would appear normal (no indication from the monitoring light). However, they would lose charge consistently afterward. If the plane sat for a week, the battery would need to be charged again before it would start the engine.

This abnormality was not indicated by the battery monitoring system (BMS). And I soon realized this was a concern.

The monitoring system only monitors certain abnormalities, but not all. This realization left me wondering what other abnormalities didn't the BMS system identify? My comfort with flying with this battery began to diminish when I understood this fact.

The other aspect of the EarthX BMS is the various indications it provides. They are - Slow Flashing, Short Flashing, and Solid. For Slow and Short Flashing you need additional data to assess the criticality of the situation. These include voltmeter and/or over-charging warnings. Depending on these indications you need to assess the criticality of the condition based on the systems in your aircraft - and distance from a suitable airport or off-field landing site.

In my case I have a both and Primary Bus and an Endurance (emergency) Bus electrical system. (I also have an everything has failed system for double redundancy but I'm ignoring that for this conversation) When assessing the EarthX battery warning light signals you need to take into account your specific electrical system to determine the seriousness of the abnormality.

Yes, of course, the solution to all electrical problems is to land right away and trouble shoot on the ground. In the real world however, landing right away is frequently not an option (terrain, urban landscape, IMC, whatever). In this case, you need a clear understanding of whether your electrical system is about to die completely.

This is where my confidence in EarthX really diminishes. The warning light system is too generic and open to interpretation. Even when I read their literature and try to apply it to my system it is not straightforward. The heart of the problem is the perception that the EarthX BMS is actually monitoring the battery. It is, kind of. For certain conditions.

In my mind this uncertainty might be acceptable in an automobile, but it's not good enough for an aircraft. After eight years I no longer completely trust EarthX batteries.

If your aircraft is not electrically dependent, then there is less of an issue. However, there will still be the uncertainty of a BMS light indication and how it may affect the flight.

In my mind, a Battery Monitoring System should be able to fully monitor all battery conditions, but this is clearly not the case with EarthX. To be fair, no other battery manufacturer does this either. I just feel there is a subtle, but important, misrepresentation by EarthX about their "Battery Monitoring System".

I do need to add that EarhtX has been great to deal with. Kathy is very knowledgeable and responsive. I appreciate EarthX's commitment to GA. I look forward to the day when a BMS is able to fully monitor batteries in all conditions so that pilots can fly with confidence.

If I had the motivation and physical ability, I would probably dump the EarthX for a more traditional battery. They are known quantities with generally predictable failure modes. However, this would mean major changes to my aircraft that I have no desire to get into. 

If my alternator fails, and the EarthX takes a total dump in flight, I have another battery backup system (TCW) that powers a fuel pump to keep my flying for some time.  

I think I didn't make an important point in my original post here.

That is, if you have a standard aircraft battery and you run it all the way down, you are probably going to have to replace it (in most cases). In this respect, from my experience, the same applies to an EarthX. The one difference may be the BMS will protect the battery enough that you can recharge it and fly yourself home - and perhaps for some time afterward as I have done. So, from this perspective, the EarthX is an improvement over a traditional battery