Charging Li-ion batteries at a constant current for a fixed time
UltraFire sells flashlights, and the batteries and chargers to go with them; this is either one of their sets or an impersonator. As the warning &quot;Forbids to invert&quot; and the fact that there is nothing physically preventing inversion show, we are dealing with a mixture of translation problems and uncertain design. I found other listings with the charger - this one on Amazon is helpful.
The charger model is &quot;UF-18650x2-charger&quot;, no datasheet found. They sell different batteries with the same charger, but this description is telling, and fits with the charger's DC output of 4.2 V, 650 mA:

Ultrafire Li-Ion Rechargeable 18650 with IC Protection [...]
Over charge and discharge protection. Protection kicks in : 2.75v and 4.2v.
Over-Charging / Draining at 4.2v / 2,75v

Another listing supports this:

The charger provide output shortage protection when battery is fully charged

The closest I can get from UltraFire is this product page for a better-looking charger (probably the original that this one cheaply imitates), which does mention &quot;auto cut off&quot;. A review of the fancier charger says:

The charger does not follow the recommended charge procedure for LiIon batteries, but it does charge to 4.2 volt and then turns off.

We can conclude the same for this rougher model based on just the listings.
So, not a high-end product, possibly a cheap imitation, but unlikely to start a fire. The original listing probably meant something like &quot;the current is stabilized to produce a consistent charging time&quot;, not that the charger will force 650 mA for several hours while ignoring the battery voltage.