Trickle charging the 12 volt battery

[Strathspey]

The online owners manual for my new (2024) Yaris cross says "Be sure to disconnect the ground before charging the 12 volt battery". I've never seen a reference to this in any posts on charging the 12 volt Battery. Why would this be necessary? Surely I can simply connect the charger + and - to the Battery terminals under the back seat, or to the + terminal in the fusebox  and an earth point  in the engine compartment.

[Dick_Dastardly]

It will be referring to a full blown charge with a dedicated charger designed to re-charge the Battery from flat

For trickle charging the current is so low that you do not need to worry 

[TonyHSD]

On 7/17/2024 at 4:12 PM, Strathspey said:

The online owners manual for my new (2024) Yaris cross says "Be sure to disconnect the ground before charging the 12 volt battery". I've never seen a reference to this in any posts on charging the 12 volt battery. Why would this be necessary? Surely I can simply connect the charger + and - to the battery terminals under the back seat, or to the + terminal in the fusebox  and an earth point  in the engine compartment.

This is to eliminate the risk of frying up the fuses or cause further damage to the car 12v system due to charger malfunctioning and high current. 
Perhaps no one does that and almost no one has ever had any issues. 
Until one day someone reverse poles connected the jump start cables and kill his car. Disconnecting the negatives terminal it’s like taking the Battery out and charge it at home, kind of safer way. 👍