mAh capacity ?

Hi guys, how can you be sure the stated capacity of a battery i.e. 4000mAh, 3000mAh etc is correct. the reason I ask is that I've seen videos on youtube showing the stated capacity is waaaaayyyyyyy short of what it says on the packaging. slab288

slab288 said:

Hi guys, how can you be sure the stated capacity of a battery i.e. 4000mAh, 3000mAh etc is correct....

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With discharge testing, such as explained here ...

http://lygte-info.dk/info/Batteries2012Info UK.html

Note that capacity will significantly vary depending upon load (among other important factors).

And, yes, batteries are sometimes labelled ... ummm ... optimistically

slab288 said:

Hi guys, how can you be sure the stated capacity of a battery i.e. 4000mAh, 3000mAh etc is correct. the reason I ask is that I've seen videos on youtube showing the stated capacity is waaaaayyyyyyy short of what it says on the packaging. slab288

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For cells from big brands like Panasonic, Sanyo, LG and Sony the stated capacity is mostly correct. For fake cells and a lot of Chinese brands the stated is optimistic to very optimistic.
You can always check my reviews and website for specific batteries, I do add a few batteries each week.

As a rule of thumb the maximum capacity is only present in Panasonic cells (Currently 3400mA, but very soon more), anybody specifying more capacity is lying. Chinese manufactured cells has considerable lower capacity. This does not mean that brand xxxFire at 3400mAh need to be lying, they may be using Panasonic cells (But mostly they are lying, again: check my reviews).

If it claims more than 3400mAh (18650), it's a lie.
If it's cheap and claims a high capacity, it's probably a lie.
A reputable seller will show the actual tested capacity.
For example, I noticed that fasttech show the tested capacity of a lot of the 18650's they sell.
They have some "Ultrafire 4000mAh" 18650's, but they state "1500-1700mAh actual capacity". And further they state that they tested a cell for QC and it had 1508.7mAh, and they state the test conditions, 1000mA discharge rate, 2.9V cutoff.
So where a really good retailer wouldn't even stock crap like that, at least they state the actual capacity.

Great thanks for that everything is perfectly clear now and I know what I'm looking for aswell. slab288

I am currently scavenging and testing some 18650's using a triton jr hobby charger. My problem is when I do a discharge the voltage the charger is lower than my DMM to the battery during load. How do I reduce the voltage sag? I'm guessing that's my problem

ACSmith said:

I am currently scavenging and testing some 18650's using a triton jr hobby charger. My problem is when I do a discharge the voltage the charger is lower than my DMM to the battery during load. How do I reduce the voltage sag? I'm guessing that's my problem

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Short thick wires between charge and battery and a good connection to the battery.
I uses something like this: