Over my past few activations I have noticed that the terminal voltage of my paired 5Ah 3C lipos was dropping under load. When re-charging, I was also experiencing some weird voltage and current effects. My Turnigy charger has a facility to measure the cell or battery internal resistance so In decided to measure my individual cell’s resistance. For all of the cells these came out at at least 50mOhm. One battery had a total 170mOhm internal resistance. I decided to purchase new batteries and this time purchase the Turnigy Graphene 5Ah 3S 75C batteries. The Internal resistance spec. for these cells is 5mOhm for 3 cells.
I measured the internal resistance of the brand new cells on completion of the first charge, They met the spec. The charging is now reliable and little voltage droop occurs on transmit.
It seems that the internal resistance is a good indicator of the “wear and tear” the cells have been subjected to.
Thanks David I have 1 cell on my 4200 LiFe testing lower voltage earlier than the other 3 cells after 4 activations but it recharges OK for now. I am hoping it hangs on a bit longer and has been in use since 2013. Done 490 Activations plus lots of back yard development work with different SOTA antennas.
Regards
Ian vk5cz …
Hi,
Old lithium cells don’t seem to die, they merely fade away like old soldiers. Their capacity declines gradually, unless abused, and it depends on your application as to whether say 40% of original capacity is enough. Is your 4 Ah battery still useful at 1.6 Ah? Is half a volt terminal voltage drop at 3A acceptable?
Yes the internal resistance rising is a sign of ageing. I think we forget what we accepted from the SLA batteries as the lithium cells were so much better.
I have retired some after nearly a decade because they swelled, not because they weren’t doing a fair job.