How Can I Know When RC Battery is Charged?

It pretty much depends upon the quality of the battery and charger. NiCd can be damaged by "trickle chargers". If the chargers are what the battery manufacturers recommend, contact the battery manufacturer. Hi end battery charges for communication radios, use a change of temperature to switch from rapid to standby. As for the Rx, you can always test it on the ground. Purchase a suitable ammeter, probably no more than 2 amps. Measure the current in standby( to measure current you need to cut one of the wires and insert the meter in series) then operate the servos and watch the current. Then using how many times you do this, you can determine how much current has been used.

Like Inverted stated, it relies upon the bettery limit. For instance a 3000 mAh battery charged at 3 amps (1C) will take 60 minutes. At 6 amps(2C), it will take 1/2 hour. On the off chance that the divider charger works at say 1 amp, it will take 3 hours.

It does take a lot of time to recharge.If only it could be recharged in a few minutes.

Battery University can probably answer all of your questions.

https://batteryuniversity.com/

https://www.rcgeeks.co.uk/blog/complete-remote-control-car-battery-guide-overview

If I were you, I'd simply follow the owner's manual instructions and use the charger they recommend. Using a different charger MAY damage the battery and void the warranty.,

Don't over think the issue.

From my experience, NiCad batteries should NOT be overcharged. They should be completely discharged before re-charging, then charged for the proscribed time. They have a memory and will degrade if not fully cycled each time.

NiMH batteries can be "topped off" without damage.

My TRAXXAS battery charger tells me when the battery is 1/4, 1/2, 3/4, and fully charged.

NiMH batteries which are regularly partially charged can develop a memory effect which effectively reduces their capacity.

To avoid this fully discharge them before charging ..... you can buy smart NiMH chargers which will do this for you as part of the automatic charging cycle.

This memory effect will not happen in one or two charge cycles, but over several hundred, so you can enjoy using your RC until you can source a smart charger without fear.

Is that ok?

Charge my RC car with another nickel metal hydride charger.

The website https://www.gensace.de/christmas that my friend recommends is doing Christmas activity, I want to buy one to try.

This thread has developed into an example of the blind leading the blind.

Burton, Do your own research, draw your own conclusions and don't listen to "your friends."

You can Google as well as the rest of us.