High Discharge Cells

I'm new to lights but just purchased a bunch of Vinh modified lights. I have Keeppower 18650 3400 mAh cells that I like but they are too long (68.9 mm) to fit in some (like the TN35vn, barely fit). I have been told by some, including Vinh to use IMR 18560 cells. Others say to use the Samsung 20R Li-ion cells. I have learned a few things about the IMR cells compared to protected Li-ion 18650's:

• IMR has lower overall mAh
• IMR (and unprotected cells in general) are shorter (easier fit)
• unprotected cells generally cheaper
• IMR chemistry is "safer" than unprotected Li-ion

But I am unclear on what "safer" means. Questions about unprotected cells (IMR and Li-ion):

1. Do modified lights have over discharge protection to shut off when battery near 2.5 V?
2. If not, how do you use these cells safely? (I assume need frequent checking with Digital Multimeter)
3. If they discharge below 2.5 V, is the risk immediate or upon recharging/re-using?
4. What makes IMR safer than unprotected Li-ion?

Thank you.

sjc said:

• What makes IMR safer than unprotected Li-ion?

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You can't over charge is the main one but you can't take that as a fact for all IMR cells, especially those with more rated cycles. There is a great thread on here that goes into the IMR cells. Should be listed in the threads of interest sticky.

sjc said:

Do modified lights have over discharge protection to shut off when battery near 2.5 V?

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Direct drive lights does have some protection, due to the Vf of the led.

sjc said:

If not, how do you use these cells safely? (I assume need frequent checking with Digital Multimeter)

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Never use them in series and in lights with boost converter.

sjc said:

If they discharge below 2.5 V, is the risk immediate or upon recharging/re-using?

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2.5 volt is not a magical limit, it depends on the actual chemistry in the cell.
This cell here can be discharged to 2 volt: http://lygte-info.dk/review/batteries2012/Keeppower IMR18650 2500mAh (Black) 2014 UK.html

Generally over discharge will reduce the capacity of the cell and serious over discharge will increase the risk when charging the cell.

sjc said:

What makes IMR safer than unprotected Li-ion?

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The ignition temperature is higher.
But how much that matters, compared to a modern cell with "heat resistive layer" I cannot say.

In fact,18650 is a model,18 is diameter 18mm,650 is height 650mm.So IMR 18650 and Keeppower 18650 have the same size.

kingwellenergy said:

In fact,18650 is a model,18 is diameter 18mm,650 is height 650mm.So IMR 18650 and Keeppower 18650 have the same size.

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650 is length in 1/10 millimeter.

Protected and button top cells is also called 18650, but is longer due to the button top and the protection.

I always use Imr cells in series and in boost regulated lights. You just have to make sure the cells are matched for series and for boosted non low voltage protection lights charge your cells frequently. It's easy