I have many batteries and not sure which is which or how old
I have been reading about how to test a batterys voltage and internal resistance using a multimeter
I was curious how people on the forum determine its time to throw away their batteries
do you use capacity testing as a proxy?
if the voltage is not exactly 4.2v you throw it away?
does anyone do internal resistance testing?
if so what ohm level do you toss it?
I mark each pair of batteries with their own special markings so I will never unpair them- and then run them until they old run about half as long, maybe 60%… Takes me about a year-ish per pair. I run 3 pair in rotation.
A simple visual inspection is often all it takes to weed out the worst of the cells. Look for common signs of degradation like damaged wraps, dents, swelling (which is rare for cylindrical cells) Check the voltage. A good cell will have a voltage between 2.6 and 4.2 volts.
I replace mine when they aren’t holding a decent charge any longer. I use mainly regulated mods so it’s not really a bother until they aren’t lasting me very long. A set of dual 18650’s usually last me a day. I just order new sets when it becomes a PITA to keep changing them.
I think I read on Mooches forum that a decent brand battery should hold up at least 700-1000 charges.
In addition to what has already been said periodically, every month or two, I pass the pair of batteries in use through the Grade Mode of a simple XTAR, discharging them as much as possible but without reaching the cut-off, so I can evaluate their full capacity. I use mainly regulated mods too so, as far as I’m concerned, I don’t need any other tricks.
I have an XTAR Dragon and an Opus charger and they both have a refresh cycle that will tell me what’s going on with each battery. I wouldn’t buy a charger without that feature again. I don’t use true mech mods either. They all have some sort of protection built in even if you can’t adjust anything.
opus was going to be my solution actually but its hard to find the opus in canada
ordering from usa would cost more than the charger itself in shipping fees
not sure what happened to shipping lately
I used to order from Illumn but then shipping jumped to almost 40$ USD - flat rate
Xtar dragon is kind out of my price range, i would rather just use a multimetre
the opus i did find dosen’t take 21700?
what does the refresh cycle tell you exactly?
all my batteries are in pristine physical condition
but old batteries go through chemical changes, build up and dendrite formation
some of mine are 5 years old and still hold a good charge in my opinion
but Im not sure I trust my opinion or if thats a good measure for safety
Yeah mine too, and have batteries 8 years old. I looked into battery testing a couple years back and the equipment needed just didn’t justify the cost, I mostly use my newer batteries and don’t mech mod…
awsome!
good to know the specific model your talking about
the listing Im looking at is the same and mentions many batteries but not 21700
thanks DMan!
You’re welcome @warkwarth. Every time, before I pull the batteries after charging, I check to see how many mah’s they took. Cells that are taking more or less than normal stand out, and then you can flag them for refreshing.
@SessionDrummer stole my answer! 
The puff counter might help you out as well. Assuming your wattage and build remains the same, check out how many puffs you you get from different batteries. If there’s a big difference, then you may consider using the lower count batteries for flashlights or other purposes. Not very scientific, I know, but that’s what I used to do before when I had basic chargers.
You can try at NKON (use the NON-EU option) cos they have the Opus BT-C3100 but you can also try the XTAR VC4SL, I use it and I like it.
I did a shipping simulation to Canada on NKON and the cost seems low, under €10, I hope it can be useful to you.
I run a mech mod with unprotected IMR batteries. I rotate them in pairs, discard them if they ever test below 2.6, and date them and discard after 3 months of use.
after some searching I found the vapcell s4 plus, it seems really highly rated on light forums and has some functions opus dosen’t
-it can charge all 4 bays 3 amps each, 12 amp total (which ill never do)
-it can run 4 different functions on every individual bay simeltaneously
-it also measures internal resistance of the cells
-same price as opus 3100
Heard anything bad about this model before I go ahead?
Yeah, that just bakes batteries lol.
I personally have not heard of that one.
Personally I recharge my batteries at 1 amp, or 0.5 when I have time, thinking about 3 amps makes me shiver! 
10 - 4 rubber ducky
me too, I almost always charge at 0.5 amps and usually no more than 93%
probably why my old batteries are doing so well
