Protected and unprotected lithium ion batteries

I sell two types of lithium ion battery – protected and unprotected. If there was a "better" type, I would sell them only, but there isn't, so I need you to choose the type that suits you best

What's the difference?

Protected batteries have a tiny electronic circuit board built into them which turns them off if they are subjected to conditions that will damage them – namely over-charge, over-discharge and short-circuit – while unprotected batteries... don't.

If this circuit is activated by any of these conditions, it's re-set when you put the battery in the charger and then the battery carries on as if nothing happened. Nice hey? 

So why aren't all Li-Ions protected? 

Well, unprotected batteries have two big advantages – they can deliver higher electrical currents (which is needed by the most powerful torches) and they are about half the price of protected cells! 

This is not a small thing. Good quality lithium ion batteries are expensive – they can cost more than a torch! You can get cheap Li-Ions but they really aren't worth owning. They don't store the amount of power printed on their labels, they don't last, and they can be dangerous, potentially burning your house down. I'm not joking – look it up! 

OTOH good quality Li-Ions – protected and unprotected – are great! The quality of the cell in a (good) protected battery is the same as the cell in a (good) unprotected battery – the only difference is that little "protection circuit board" or PCB, which adds a lot to its price (if it's also good quality).

Looking after your Li-Ions

In most setups, the greatest threat to the life of a Li-Ion is over-discharge. Many people don't know that if you run a Li-Ion below a certain voltage you will destroy it (they are a bit like car batteries in that respect). They normally operate between 3v and 4.2v (even if they say 3.6v or 3.7v on the wrapper) but if you run them below 2.6v they will be permanently damaged. 

All Sofirn torches have a low-voltage cutout feature, so the torch will cut out before the voltage of the battery reaches the point of no return. Sofirn's own-brand batteries are unprotected, very good quality, and exceptional value for money.

However it's important to understand that most modern torches – including Sofirn – have a very small "parasitic drain" even while they are in standby, so they drain their batteries even when they're turned off or locked out electronically! This means your batteries could be trashed after a few months of storage – or less, if they're not fully charged to start with! 

For this reason it's vital to lock out your torch mechanically – usually by unscrewing the tailcap half a turn – when you put it away. If in doubt, remove the battery and store it separately. If you're not sure that you'll always remember to do this, or you have another brand of torch, you would be well advised to buy protected cells.

The short version

If you make sure your Li-Ions never run below 3v then you can safely use unprotected batteries – and save yourself a bundle of cash! Pretty much every torch will warn you when its batteries are approaching 3v by flashing its beam or showing a warning light. 

The big thing is to charge your battery after each use – don't wait for the red light or flashing beam (Li-Ions last longer if you keep their "depth of discharge" shallow) – and then lock it out mechanically, or remove the battery. If you're not sure how to do this, drop me a line at

Last word

If your torch has an electronic switch, it will draw power from the battery even when it's turned off. Left long enough, a protected battery will run down until the protection circuit is activated and it will need to be recharged before use, while an unprotected cell will run down to the point that it's only good for recycling!

You can avoid this by always mechanically locking-out your torch OR removing the battery when it's not in use. But if you are entrusting your torch to someone else, you would be well advised to spend the extra on protected cells like Keeppower, which are much more forgiving and come with a one-year warranty. 

If you are still in doubt, please drop me a line (at and I'll do everything I can to help.