Hello.
I have one similar battery like this one on the link below laying around. But i can't find the original charger.
I have another 12v 4A Plug here, so i am wondering if it is safe to charge the battery with this.
The chinese seller says it is no problem.
Can i trust this or is it dangerous?
Thanks for your help
No, it is not safe. For a couple of reasons:
Generally speaking, charging lithium is already dangerous because it's not trivial to do it correctly but
Since lithium's nominal voltage is about 3.7V, and you have something in the neighbourhood of 12, there are probably 3 in series (known as 3S). This means you need a charge ballancer, because without one, one cell will exceed its max voltage before the others and you'll have a fire.
Since your "plug", which I take to be an AC adapter, is not a "smart" device, it will just dump as much current into the battery as it wants according to ohms law until the batt voltage approaches the charge voltage. Since most lithiums can't tolerate a charge rate higher than 1C, again, you will have a fire.
Without any means of measuring, cell voltage, pack voltage, charge rate or temperature, you will probably over-charge the battery (above 4.2V) and again, you've got a fire.
In other words, don't do it. If you told me you had a Ni-Cd battery we'd be having a different discussion and I'd say go for it but with lithium, no.
Concur with Gahhhrrrlic.
A '12v 4A Plug' means very little to me, it could be anything.
Lithium batteries can and do explode very violently if you get the charging wrong, I narrowly escaped loosing my sight (and it could have been far worse) when one exploded in a large fireball a few years back.
If you want to charge a Lithium battery, buy a charger that is explicitly designed for the job, do not use random power supplies as a replacement.
Almost lost your sight from proximity to the explosion itself or the brightness of looking at it? Just curious...
Gahhhrrrlic:
Almost lost your sight from proximity to the explosion itself or the brightness of looking at it? Just curious...
I was sat in my workshop, as I am now, looking at my PC screen.
On the shelf to my left, around 50cm away, I heard an odd noise, sounded like pressure in a bit of plastic.
I looked up and a Lithium battery I was charging, 3S 1500mah, was bulging, odd I thought. I grabbed it and threw it out the door.
It exploded in a large fireball before it hit the ground outside.
Thanks a lot for the answers.
So i won't charge it.
But does this mean that almost every one of them will explode, it's just a matter of time?
Because they sell a ton of these on aliexpress.
I also can see that the "CE" logo is faked.
Suigor:
But does this mean that almost every one of them will explode, it's just a matter of time?
Perhaps you did not understand. It will not explode if it is charged correctly.
Lithium batteries explode, essentially because of material failure... the membrane that keeps the reactants sealed off from the outside air and the electrodes from each other. If any of these membranes are perforated or sufficiently degraded from use, you can have a fire/explosion. I suppose if you use the same battery forever and ever, you could have an accident with it, using it properly but most lithium batteries outlive the electronics they are installed in so that tends not to happen. Only people like me who keep their phones for 10 years because they didn't drop them and don't care about flappy birds v21, are at risk of batteries failing for no apparent reason. Otherwise it's abuse or negligence that causes problems, as indicated above.
srnet:
I was sat in my workshop, as I am now, looking at my PC screen.On the shelf to my left, around 50cm away, I heard an odd noise, sounded like pressure in a bit of plastic.
I looked up and a Lithium battery I was charging, 3S 1500mah, was bulging, odd I thought. I grabbed it and threw it out the door.
It exploded in a large fireball before it hit the ground outside.
Talk about luck...
Was that a random accident or were you doing something incorrectly with the battery at the time?
It's good to store those battery packs in bunker boxes. Also, when charging them, it can be beneficial and a good idea to put them in a purpose-built metal box - in case anything bad happens during charging.
If the battery was manufactured poorly, or designed poorly, or has some kind of manufacturing defect, or was operated outside of its limits before ..... then that's something else to take into consideration as well.
We should all go back to Ni-Cds. I'd rather have 30 minutes of talk time than a fireball scorching my nuts off 
Gahhhrrrlic:
Was that a random accident or were you doing something incorrectly with the battery at the time?
I was never really sure, there was no 'evidence' left.
However something went wrong with the charging causing it to continue to accept current, presuambly beyond the point of full charge.
If you hang around here long enough you will see many people assuming you can treat Lithium batteries like NiCd or Nimh, not worry about letting them go flat, assuming the so called 'protected' cells are inherently safe, use a hookey charging method etc etc.
Most of the time you might get away with it, but every now and again you wont, as indeed Samsung discovered recently.
I did once try to destroy a NiCd by putting masses of current into it; it did get hot and eventually stopped working with very dissapointing and very quiet 'fizz'.
Southpark:
It's good to store those battery packs in bunker boxes. Also, when charging them, it can be beneficial and a good idea to put them in a purpose-built metal box - in case anything bad happens during charging.
Indeed, in a previous incident I almost set fire to my wokshop, a LiPo was chaging on the bench and something went wrong.
The large (1500mAhr+) RC model ones I now charge in one of the fireproof bags and even that is on a stone tile.