how many .img files can be used at time?

thanks

it is just somehow difficult to interpret

So now I understand it is more about the data amount in all the files rather then the number of files?

just to explain: the 62s and 64s have a SD with 12 OSM files and can handle up to 4 if thse files. The other have to be renamed.

66i shoud have 5 times more ability, but it can not handle the same amount as the 62s and 64s

This is why I am confused here.

I believe that is true. Segments are what gets indexed (as I understand it). But I don't really know much about maps. Deferring to atlas_cached

Perhaps this question should be asked over there...

So far as I am aware, other than the additional inReach features, they are all the same devices.

The GPSMAP 66 series does index 5x as many map segments as the 62/64/65 series devices.

that is what I also understand.

Practice shows me different, in fact the same SD which runs fine in 62s, does not work same way in 66i. OK, it might be because the 66i has already some map files pre installed, but it is difficult if not impossible for the user to find out how much of the 'segments' (what ever this means) have been used. Or is there some way to find out?

As indicated elsewhere, your issue is with the third party maps you are loading to the device. There is nothing wrong with the 66i.