purple efest 18650 2500 mAh battery question...

[Ellipsis]

hello folks...
just bought these from the b&m i have used for 2 yrs...
box says efest imr 18650 3.7V Li-Mn Version 1 flat top 2500mAh

they were removed from the boxes, inspected and placed in the battery charger (xtar vp pro 2 bay)
they read 3.6 v and charged to 4.2v (at the 1.00A setting)

1 battery was placed into an ipv 2 with the wattage set to 20 watts
(magma rda , dual coiled for a total resistance of 1.1 ohms)

the ipv2 read the resistance as 1.1, when fired the display indicated 4.8 v was being applied...
at the end of the day i noticed the battery lvl indicator showed the battery level was down to around 1/4 left...
also when i pressed the fire button the battery level indicator dipped to show no bars inside the indicator...

is that what you all refer to as battery sag?
is that bad?
is that where i need to remove and replace the battery with a fresh one?

this has never happened to me when i use aw imr 18650 3.7V 2000 mAh 10 amp batteries in the same device at the same wattage with the same rda

some help understanding what is happening

i understand that 4.8v applied to a 1.1 ohm resistor results in 4.36 amps and a wattage of 20.95
so the ipv2 isnt exact
but im not stressing the battery or coming any were near the amp limit of either the efest or the aw...
or am i?

 

[Lefty]

As I understand it yes is does show battery sag. Does it also drop the wattage when this happens? That Efest is purported to be a LG18650HE2 under the wrap. That is a 20 amp continuous and 35 amp pulse rated battery. If so then no you aren't near the amp limit. However, if that is a knockoff Efest (your B&M wouldn't necessarily be aware of it) then there is no telling what the amp limit is. There is a thread or two here on detecting fake Efests and more I'm sure can be found on Google. If it were me I'd look into it.

 

[Kemosabe]

also consider that unused lithium cells will need a break in period of a few charge-discharge cycles to reach their full mAh potential.

 

[dr_rox]

Battery sag is what is experienced when you put a load on a battery and the sag is the voltage drop.
The sag is the product of the time it takes for the reaction to liberate the stored energy demanded by the circuit.
You see this in your car when you put the headlights on, then try to start the car. A good battery will only dim the lights a little. A bad one will not start the car at all.
To figure out if you got the mah you expected, do the math. MaH is milliamps x hours. 2500 mah will give you 2.5 amps for an hour. Roughly a 1.6 ohm coil on a mech will give an hour of use. Efest batteries are relabeled old stock that meet a minimum criteria. EG, in hand I have a 3000 mah 26650 efest. Pull the label off, manufacturer rating is 3500mah. Why? Possibly someone found a stash of uncommitted old batteries in a warehouse, then took a representative sample and found many batteries didn't achieve this, but were at least good for 3000 mah. As far as life goes, these batteries do have a shelf life but until someone figures out the 'born on' dating system, we may never know how old they really are. Those batteries could be several years old, at or near their end of use date. There are born on dates on IC's, so if there is a bad run they could all be called in. Should work the same way with batteries. Sometimes there is data stamped on unjacketed cell, but haven't figured it out.