Series batteries - dropping too low?

[sterling101]

Had one little issue over the weekend where the voltage didn't hit cut out until 3v was sensed via the voltage divider but when I pulled the batteries and checked each one with the meter and one had hit 2.5v whereas the other was at 3.5.  Now I know these are the batteries aren't the brand new set, but they're not that old either (about two months old).

Just concerned me that if I have a cell that's got the slightly different discharge curve to it's pair I could end up causing damage by discharging too far.

I know the perfect solution is to use protected cells, but wouldn't this end up causing problems of cutting out if there happens to be a drain point that takes it below the 2.7v cutout briefly?

Not sure what's going to be the best way around it really.  The ones I was using are Ultrafire LC16340 880mAh (blue batteries) and they have both recharged ok and after 2 days are holding fine at 4.02v.  I've seen various different reviews showing the actual capacity of these batteries anywhere from 680mAh down to 390mAh so it seems they're not really overly consistent at all.
The other set I've got running are some DLG ICR16340J 600mAh and they actually came free with a battery holder I bought for using on the test rig but they seem to get pretty good reviews.

So, I suppose the main thing would be is the solution to just go for much higher rated batteries (18350 IMR) or alter my cut out voltage to hit harder which means if there's a drop below cut of include a counter to ensure it's not just atomizer drain pulling it below the cut out.

[Breaktru]

I've used series batteries for a couple of years with the OKR, 08100w, 08060w and an LDO06c and it's usually the bottom battery that dischargers to a lower voltage than the top battery.
I've experianced this with all types of batteries including IMR's and CGR's

[sterling101]

Been mulling over a method of checking the cells individually but in a tube mod it's just not feasable.

I think I'll just live with it and hope I don't kill the cells for now.  If I switch to IMR 18350's I can get as low as 2.5v discharge anyway and not worry so fingers crossed it'll be all good

My low batt cut off is set to 3v anyway so it shouldn't drop out too bad unless it's a bad cell.  Went for 3v as it's a half voltage readout from the series pair and my max Vout is 6v so it keeps it from not being able to provide the volts it needs when it needs it

Next job is to stop it from having fit at me when I pull a bit much under load from the batteries - need to have a counter register so it will only shut down if the voltage stays below 3v instead of just dipping down under heavy load...

[Breaktru]

The mods I described have easy battery access so swapping battery positions half way thru is easy.
On my Series vape - Parallel charge mod, I occasionally switch over to parallel mode which equalizes the two batteries.
My last DM mod, I monitor each cell but like you said, a tube mod would be hard to do it with unless you can squeeze in a flat ribbon wire between cells.