Lower voltage after use on 2 cells

[Elmarkro]

Hi.

Im running 20S 2P lipo. I have a LVC at 3.7 per cell. I have 4 5S pacs in series ans the 5 cells in the pack on the end of the stack have lower voltage than the the rest. Im reading 3,7 at 15 cells, 3.5 at 4 cells and 3,1 at the cell at the end. I have excactly the same resaults when i meassuring the other 20 cells in paralell.

I have been using this batterys for 7 months without any issues. Does anyone know what can be the reason for this? Is it dangerous to continue using this packs?

 

[wesnewell]

How are you charging your 20s pack?

 

[Elmarkro]

Im using 2xTurnigy 4 channel charger/balancer. So unill I get a bulk charger im balancing my batterys on every charge..

 

[dogman dan]

Chances are, you are losing capacity on that end cell for some reason.

End cell, the one that gets dinged? I'd seriously suspect physical damage. Bet it's got a dent, or even a hole in it.

If it's not damaged and ready to fireball, then you at least have to stop discharging when that cell reaches 3.5v.

Even if inspected and deemed safe to use, I bet it's got really high resistance, and is causing sag. You may be using it at a c rate that exceeds its current real world c rate. In other words, if it's sagging and sucking, it's not 20 any more.

Time to buy a new pack, even if just a 2s pack to get new cells out of or two single cells. I'm assuming you have two cells gone bad, since you are running 2p.

Wait a minuite, maybe I got this wrong. One entire 5s pack has all the cells low? If so, maybe the whole pack needs a replacement. You can ding all 5 cells easy, if something is whacking the bottom of the pack, like a screw to bolt on the battery box.