Is there any harm to charge the battery without removing the cables

As long as the key is not in the on position ..you are fine

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Depending on the type of charger: I do have a ctek, that uses a desulfation process (current spikes), maybe no the best for vintage electronic (ignition, audio, etc...). On a modern car, should not be an issue, except that the modern design is probably damping the current spikes and hence somehow reducing the efficiency of the charging process.

To be honest I would not bother unless the charger is really delivering a high output (more than 10 amps).

 

If you have a shut off switch it won't be an issue.

 

The switch is not a one fit all solution :

If the OP has a car that is not supposed to be jump-started one can presume some delicate electronics are involved. Large capacitors do not like to be shut-off and reconnected. On vintage cars, audio amplifier and ignition noise capacitor are very sensitive for sure. Modern cars can be even worse: many components are always on, and may (or may not) endure repetitive current bursts.

Kill switch used to be standard equipment and were removed for good reason: disconnecting the battery while the car is running can have catastrophic consequences for the onboard electronics. I just learned it the hard way when the lady accidentally bumped the switch (on the 365 it's on the footwell...): the unfiltered alternator ripple was mixed together with the RPM signal which toasted the 365's tachometer (it jumped to the maximum).

Certified FIA switch do have a built-in resistor that helps mitigate this, but for long term storage you need a secondary switch to cut-off the resistor, which makes it a bit messy. If the OP want to charge with a powerful workshop charger, that's what I would use.

 

When I have a car I am working on and will be doing a lot of diagnostic work, I have it on a charger. Key on, key off, checking parameters and errors, I need good battery voltage and a charger keeps it strong. I have never had an issue. I also use a vintage (80s) Schumacher charger. It is not like the modern safety chargers, this thing just charges. Plug it up and it will bring a battery back from the dead. I am pretty sure it would charge a brick if I could hook it up.