Under performing LiPos

[Ian_Gsi16V]

I managed to find some RC time at the weekend, sadly, not all is well! 

I have two lipo batteries that seem to have lost some punch, both 2S 4000mah and different brands, both will happily balance charge to full and storage charge no problem but after 5 minutes of run time they are tripping the low voltage alarm and they don't have the punch they should even when 'fully charged'. 

Neither battery is puffed at all and all my batteries are always balance charged and have never been ran under 7v. I think they have been sat for around 3 months without usage, I can't say they definitely had a storage charge as it wasn't really an intentional RC break...

Any ideas if they can be brought back to life? Any tips? 

[MadInventor]

Maybe try a different charger. It could be the charger falsely detecting a full charge. Also check that there is not a time limit on how the cells are on charge for. A friend of mine got caught out with that, charging 5000mah cells at 0.5C with a 4hr time limit set. Cells were no where near charged as they timed out before being fully charged.

Speaking from my own experience, I've left LiPos fully charged and unused for over a year and not had any issues with them, likewise left some for months partially charged and they have charged ok afterwards. If it's 2 different makes that have failed I'd definetly be looking carefully at the charger.

 

[TheMidnight Pumpkin]

I agree with MadInventor, I would think its the charger. I own a Hobbico charger that false shuts off sometimes, which equals packs that are not fully charged.

Also the puffing thing is not an issue on all brands. Its mostly the cheaper Turnegy packs that fail in the massive puffing until they short out internally. Some lipo brands never seem to ever puff, even when abused.

Lately I've been using the Floureon brand lipo's without any problems. I've been getting nearly double the flight times in my RC planes with them when compared to the Turnegy packs. The price is also comparable for the better quality.

[Ian_Gsi16V]

Thanks for the input guys, I would agree with the charger issue but I have other lipo batteries which are still charging and performing exactly as you would expect it is just these specific two out of my set of batteries.

I would try another charger but I don't have access to one, would be cheaper to just buy two new batteries 

I tried them a couple of times at the weekend and they did seem to get slightly better after each run so I might give them a very slow charge at 1C and then give them cycle them a few times. 

[Wooders28]

2 hours ago, Ian_Gsi16V said:

I might give them a very slow charge at 1C 

I was under the impression that was the max you were meant to quick charge lipo's anyway!? 

[Ian_Gsi16V]

1 minute ago, Wooders28 said:

I was under the impression that was the max you were meant to quick charge lipo's anyway!? 

Sorry, wrong terminology from me, I meant 1.0A. 

Batterys are 4000mah so I charge at 4.0A. I only ever balance charge, i'm never in that much of a rush that I require a fast charge.  

[MadInventor]

4 hours ago, Ian_Gsi16V said:

Sorry, wrong terminology from me, I meant 1.0A. 

Batterys are 4000mah so I charge at 4.0A. I only ever balance charge, i'm never in that much of a rush that I require a fast charge.  

I always  balance charge mine at 0.5C or less, takes ages, but the cells never get warm when I charge them, and so far, fingers crossed, no failures.

[Ian_Gsi16V]

I'll give a slow charge a go and see what happens and report back  

Just need to try and find time to run the car again

 

[danb1974]

Don't hold your breath

Lipo does not give false peaks, they are charged CC/CV until each cell is at 4.20V and does not draw current, end of charge is very precise. When their internal resistance goes through the roof, they are no longer capable of delivering high currents, you hit the throttle, they hit lvc.

Charge in balance mode, make sure no charger timeout occurs, give them a few cycles but don't expect any miracles.

If you store them fully charged you can loose up to 40% capacity per year. Also avoid storing in hot places.