Hi. I bought two mosquito killer lamp.
I noticed that charging was taking too long, so after charging stop and blue lights disapear, I went check battery with multimeter and I seen it's been overcharged, 4.50v+.
I checked other lamp, and its same!
Device have protection for overcharge, because it stop charging at some time, right? So, why not stop charging at 4.20v?
Btw the battery inside 800mah was gave me only 4h of working. So I replaced with my battery 3400mah. Now hold 20 hours!
If that's the real voltage (multimeter works correctly) you should get rid of those lamps and batteries. They are in dangerous state and can get on fire any moment.
Check your multimeter first. It's not uncommon that cheap multimeters show the wrong voltage when their internal 9volt battery is almost dead.
Leo..
Batteries are very good.
If you track my last threads, you can find that I bought a new and good multimeter.
I made a picture of the old and new multimeter measurements to prove it to you. If you do not believe I have a third multimeter and a few quick voltage meters and can measure with that.
This picture is of my replaced battery, but overcharged with this lamp 4.57v.
Also, the lamp overcharges the 800mAh battery, which came with the lamp.
My regular home charger never passes 4.20v on those mine Liitokala batteries.
There probably is no charge controller at all. They probably just set the voltage to 4.5V and use constant voltage charging, it the cheap way of charging a battery.
You bought two pieces of junk.
That's a horrible business. I will send them feedback.
Charging stop at some point and charging light turn OFF. Maybe there is some charge controller, but placed by default or for the wrong type of battery, not for 18650.
The best way is to watch the clock now! Don't let the battery pass range.
The second question is:
That all similar lamps are described like 1000-3000 volts. Why is that? Is that because "mosquito fill" 3000 volts on itself?
And why my multimeter show 360 volts then, when touch two wires (mosquito kill), but it is not really that much, because I can touch it with fingers (someone touch with tongue I saw). And I know how strong is real 12v on electric fence energiser, it's really hurt.
Picture show of touching two wires which kill the bugs. Voltage says 360. Is that maybe something to do with AC / DC current?
I suggest you not to use your multimeter to measure kV range voltages.
And I wasn't kidding about the safety of your batteries. At 4.57V they are overcharged ~110% and not safe to use.
You meter is loading down the circuit and I'm sure it's not a constant 3000V but pulsed so your meter can't read it
This is the lamp I bought:
https://a.aliexpress.com/_EwbZLby
They are 60 Feedback with pictures. And there is only one, which says that
battery discharge to 2.5 volts and is not safe! That I didn't notice.
Yes and what to do now? Throw it? They are still working. Other people who bought those items are still charging them every day...
That's bad as well but not as bad as noticeable over charge.
Most fences give a shock ~5000V, it can be powered from 12V though.
Really?
Sorry, I am confused now more than before 
Well, 220v from the wall kills you instantly (in most cases), right? So why not the same on that fance or this lamp?
Current kills. And time is crucial factor as well.
That's why we use protective devices on mains, RCCB, that trips if current goes above 30mA and time 300ms.
The pulse from electric fence is low current and duration is less than 1ms.
You are using the 250vdc range to measure 3kvdc and the reading is negative 360vdc. ("APO" indicates auto-power-off is enabled)
And this...
From the IC markings, can you identify whether there is a charge controller IC fitted?
If so its datasheet might identify a way of setting the maximum voltage.
There might be a 'select on test' resistor that you can change.
I'd already noticed from the second photograph in post #4 that danyCro doesn't care which way he connects the probes: -4.57V indicated.
That is a good idea! I will send a pictures.
Yes, because always show the same, positive or negative.
I don't have now overcharged battery to try charging in the opposite way. 
But can charge "kill" wires around.
no, 220 V from the wall does usually not kill instantly... but it may do so...
Do you want to destroy your multimeter???
Nice try!
it is definitely not made for kV range!
