do i have a dud Lifepo battey?

[salmirabile]

I bought this battery the other day:

https://www.ebay.co.uk/itm/12V-20Ah-...72.m2749.l2649

My problem is this....I understand lifepos aren't meant to change voltage very much until almost depleted but under some load of 4a which equates to around 0.2C, the voltage drops like a stone to 11.2v!! Is that normal or do i have a fake/dud battery?

Also, after a full charge at 13.8v, it goes down to 13.4v after 10 minutes without any load and then after having the 4a load on for around 30seconds, the voltage reads 13.3v which is 90%...how can this battery lose 10% in 30 seconds?

[PNjunction]

That's normal to see that quick drop after stopping a charge on LFP. - and you haven't lost 10 percent.

If you are using a charger going to at least 14.6v, when the internal bms decides that the battery is full, it will disconnect the charge source. Terminal voltage falls real quick to about 13.6v or so. If you wait about 12 hours, that falls even further to about 13.2v

In fact, if it didn't do that, then you'd definitely be in an overcharge condition.