You unhook both batteries at the sametime because they are hooked up in parallel if you don't you will get back feeding.

Yes the computer has to relearn anytime the batteries are disconnected.

Hope this helps

 

You can change them 1 at a time in the parking lot of the store, or at your shop and then return the dead batteries for the core deposit. Simply remove the negative cable first and then the positive cable. I stick the positive in a beer Koozie once it is removed while I swap the battery to keep it from touching anything.

The other option is to get a memory saver and plug it into the lighter while you swap the batteries.

 

Just an FYI. This will work but be careful not to cause any arcing as damage to the computers do to voltage spikes can occur. As jbullfrog said Positive cables will be hot always with this method.

Proper procedure for un-hooking dual batteries is:
1) Disconnect Ground cable at Secondary Battery (LH)
2) Disconnect Ground cable at Primary Battery (RH)
3 Disconnect Positive cable at Primary Battery (RH)
4) Disconnect Positive cable at Secondary Battery (LH)

Reverse this procedure for hook up.

I personally have never had good luck with these on late model vehicles do to the high voltage requirements of all the components that are "always" on. The little battery supply is just not enough to retain the computer memory.

 

If you change 1 battery at a time be sure to insulate the positive cable end so it does not short out. we use large rubber sleeves when changing batteries one at a time, especially on vehicals where batteries are stacked rather then side by side.

 

I just had two of Ford's best batteries installed. Three year free replace, 100 month warrenty and Free towong for battery problems (at a dealership) for the full 100 months. Total price $182.00.

Mac

 

Cost me 170 for both, good idea to change both...IMHO