It is inexpensive RCA plugs which you may solder without problem.
Most other cheap RCA plugs I bought on ebay so hard to tin and solder, so you can melt internal insulator first.
This ones were soldered like breeze!
10pcs 5V Mini USB 1A 18650 Lithium Battery Charger Board Module TP4056 TE584
21 September 2017
Excellent thing!
I transfered all my flaslights from stupid 3xAAA to "free" lithium cells from old cellphones using these chargers. Just adjusted it for 300 mA charging current by replacing current set resistor from 1.2k to 3.3-3.6k.
Good set of 4 batteries. Charger works bit strange with all connected 4 batteries - all 6 leds turns on when input voltage drops at full load. But it charges good.