I have a six-month old P4-RTK with about 20 flights on a particular battery, so lots of life left in it.  Right after takeoff the other day, I got a message on the RTK controller that said "Battery is damaged", with all sorts of red flashes.  I envisioned my investment falling out of the sky, but I was able to land it - immediately - with no issues.  Examined the battery, looked good, reinstalled and checked connections, and took off again; this time no higher than six feet.  After five seconds, same "Battery is damaged" message.  Removed battery, looked at the Airdata record, which I've attached here (file name ends in 012020).  So I figured my smart battery was now just an expensive paper weight.  But Airdata also told me that it was time for a basic service on that battery, which is just a deep cycle (deplete to 8%, then recharge).  So I deep cycled it, then took the risk of CAUTIOUSLY flying it again for a few minutes.  Worked fine, and wasn't hot, so flew it until 28%, then brought it in and looked at the Airdata record again.  All cells are perfectly aligned, as shown in the second attached file (file name ends in 012320).  So all that just to say that if you get a "Battery damaged" warning, with really ugly current deviations, it may not be the total loss that you think.  Try deep cycling it, and see what happens.  But you may want to keep a close eye on it.....

Hmm, interesting. Didn't think about doing an early deep cycle to "restore" or reset the battery so to speak and essentially reboot it. I have a P4P battery that did exactly the same thing after 14 flights. I figured it was bricked after my Airdata showed the current deviations. Good to have a data point from you on this, but interested if anyone else has some input this? One data point does not equal a trend ya know? :-) Thanks!

I suspect that 'deep cycling' the battery does not have much effect on the battery, what it does do though is rewrite the values in the memory of the smart battery controller, putting it back to normal status.

Definitely agree - not necessarily a trend, and I'll also be interested to see if anyone else has a similar experience.  But - as Robin Williams once said about golf - it's just enough to give you hope.

I run mine down to about 6% every 10 0r 12 flights.  One is over 2 yrs old.

I've had P2 batteries for which I was getting warnings were out of balance and when I did the deep discharge, it seemed to fix it.  BUT, as it turned out, the fix was only temporary - like two or three flights.  Something like that.  Regarding the 8% rule, the repair/maintenance was not to 8%.  The rule was BELOW 8%, per the manual.  I've seen 5% and even 3% quoted by mods on this site.  Oddly, they don't talk about it much these days.  Congrats on repairing your battery but keep a close eye on it.  

Good luck

I do this every so often, battery 1 is 3 years this summer, thats the main battery and has the most flights, the other 3 will be 3
years around autumn this year i think it is.

After 10 or so flights i will just let it hover at 10%,  and prevent it from auto landing, this lowers the percentage faster, once i have
no choice and it lands, i then restart it in the ground and let the props run till it shuts down, then i charge it

Geebax, whilst you say it has no effect, in effect it does, even if its just rewriting the values, its certainly doing something for the
battery, put it this way, had the OP not done this, his battery would be dead weight

Bashy Posted at 1-25 23:24
I do this every so often, battery 1 is 3 years this summer, thats the main battery and has the most flights, the other 3 will be 3
years around autumn this year i think it is.

Great info, @bashy.  I'll make that a regular practice at 10 flights.  Thanks for the tip.