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EVO II battery instantly went to ZERO!

For the second time in as many months, I had a battery instantly drop from about 50% to 0% and the EVO II did an automatic landing. Unfortunately, it landed in the river. The battery had about 90 discharge cycles on it and the last battery that failed also had about the same number of discharge cycles. I expected I could get about 200 discharge cycles out of these batteries since Autel warranties them for 200 cycle within a year after purchase. Both of these batteries were about a year and a half old so they were out of warranty.

My question is, should I just discard an Autel EVO II battery when it get's 90 discharge cycles on it? What has been the experience of others here with these batteries? Prior to each failure, there was no indication what so ever that the battery near the end of its life. However, interestingly, on both flights, I noticed the battery was just over 50% right after I started the flight. This was unusual because I normally charge the batteries after each flight. I assumed I forgot and kept flying but planned to keep both flights short. Of course, I wasn't expecting the battery to suddenly go to zero. I'm wondering if perhaps a sign of a faulty battery is when it looses about half it's charge within a couple of days of being charged. I don't know for sure that the batteries had been charged but I'm about 90% sure they had been. I fly frequently and don't recall ever forgetting to charge the batteries prior to flight and the only two times I noticed the batteries were already almost half discharged, both batteries instantly went to zero within the first two minutes of flight.

The video of the crash was corrupt but I was able to recover all but the last few seconds. If anyone is interested, here it is:
I added stock footage at the end to simulate the crash.
yep, same hear, batteries are about 2 years old, max 50 charges. shows 100%, then drops to 0% within 5minutes. But then press the button on the battery and has all LED's are lit. Must be dodgy cells.
 
There have been many posts and threads in and around this forum regarding battery life and care. And it can turn into a rather technical discussion quickly. I won't go there, but feel free to do a search in the event you want to drill down and read a lot more about it.

A few takeaways I've adopted from reading the other thoughts here are first and foremost, I try not to leave my batteries in either a fully charged state, or a fully drained state any longer than necessary. I heard somebody say leaving your battery fully charged is like keeping a rubber band stretched to its limits, and over time the band wears out or snaps. So when I know I won't be using a battery for a while, I will try and leave it resting around 50% charge. This hopefully extends its life. Of course the design allows the batteries to self-discharge as well after several days, but I'd rather not wait for that if I don't have to.

Next, when charging, NEVER pull the battery off the charger before it is completely finished. Even when all four LEDs are lit, wait until they go off as the charging process is ongoing with balancing the three cells inside the battery. And that brings me to the final point.

Every time before I fly, I always go into the settings and check the battery health to make sure all three cells are reading equally, and there isn't a weaker/bad cell present. Obviously if there is, don't take off. Either put it back on the charger or discard it.

I can't really comment on what should be a reasonable expectation for cycle count (50? 100? 200?). I do tend to start getting nervous after 50 cycles, but that's probably just me. I don't think I've ever surpassed 100 since my paranoia just gets out of control by that point.

Hopefully this helps, very sorry you lost your drone in the river, ugh!!!
 

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