Got a new key fob from merc. Thinking old one was not working. New one will not lock doors. no nothing only valet key will lock and unlock. Ignit part of fob on both new and old key work. suggestions?

Because you removed the fob battery and further compounded by the fact you disconnected the vehicle battery, the complete lock system and the anti-theft immobilizer system needs reprogramming. I am undecided whether a locksmith or an electrician is better, but would suspect the auto locksmith.

https://www.google.com/search?q=mobile+auto+locksmith+near+me

https://www.google.com/search?q=mobile+auto+electrician+near+me

The car should always be started with a proper chipped key. The valet key on my car has a chip in its credit card style case. It will start the car if the case is close, or you can give the key to someone just to gain entry to the car and not start it.

this is Australia's cheapest car;! we have no books on down under cars.(generic answers me, outside USA)
lost 2nd FOB?
and cars mostly have key that can open doors. even a key hiding in the fob.
or valet key?
the fob has a battery too on most fobs. a coin cell
lost the users guide? in the glove box.

car battery not put in backwards correct, Plus to Plus only !!!!!
head lamps on car work>? yes./no
try both fobs cars come with 2 never just 1,
some have valet keys too.
most have a fob battery .
12 year old fob coin cells are EOL this old end of life where present,.

Where else do you have locks? A locking glove compartment often has a separate key. The main key is supposed to open the door, open the trunk and start the vehicle. The other key is a Valet Key, the key is intended for people to give to valets to park their cars or to repair shops to use. The valet key will open the car door and start the car but will prevent someone from unlocking the glove box or the trunk.

notify manufacturer about your after market ''valet remote starter'' system like with any remote start system they are tapped into your locking system and can cause havoc or disable it so you can ask them about your problem

You may be trying with a valet key.
Valet keys usually can unlock the driver's side door and start the car, but can't unlock the trunk or the glove box. This key is normally used when someone else operates your vehicle, such as a valet parking attendant.

valet switch?????????????????

When the anti theft system was created,the dealers forgot to tell the new car buyers about how much the fob matters to the vehicle,without it,owners are stuck,your anti theft device is activated,you need to lock and unlock your doors a couple times with the key fob,not the key,and then you need to put the key in the ignition and start it,if you dont have your key fob,call your car dealer to get a new one,they are programmed for each car only,you cannot bypass it.if you lost your fob or never had it,whatever,you need to have the exact fob that came with that car from the factory,the key and fob have a chip in them that only go to that certain car,if you do not have it,then you need to buy a new one from the dealer or ebay and then you need to contact your dealer about programming the fob to your car,you might not have to have it towed if they have the documents from the car,the only other way is to get a junk car,with the steering column,key,fob and all computer boxes and door locks and switch them,i just did that with a 98 dodge dakota,and it works.

more than likely as the fob key has a chip that syncs with the security system etc , have you got the owners handbook as this should give you the procedure that needs to be carried out to reset the fob key,can't take the credit for this fix as found it at an audi forum give it a try .
I learned a new trick tonight. I recently changed the battery in my key and it would no longer open the door locks. I just sat down and read the manual and found that if you replace the battery you need to re-synch the key.

Here is how it's done.

replace the battery. ( pry open the little tab at the seam in the key, then split the bottom in two with your finger)

Press the lock or unlock button once.
with-in one minute put the key into the drivers door and lock and unlock it manualy.

TADA it works again

I have seen a few threads and questions that said there fob stopped working. so I thought I would throw this out there. I hope that some of you with this problem that don't have manuals because the previous owner kept it for a souvenir will find this Helpful.

there are 3 ways to lock.
key metal
on door switches
and the FOB, RKE.

so is this a fob question? key fob? only failure???????
did you know that many fob modes are PROgrammable?
the operators guide tells you how to do that.
did you try both fobs, that came with car new., if not why not?
did you replace the 8 year old fob batteries, no , why not now.?

on my 08 (for example) :
can program it to only open drivers door. or all.
and autolock feature off or on.

on my other car all was worked fine. then drives door failed
to open (all 3 fobs fail, one is new) the door solenoid was bad.
$100 part. now fixed, by me.
so do all fobs fail. if in fact this is a FOB question
RKE (called remote key entry by jeep)

i have 4 fobs for my jeep now. you must have 2 good keys.
to make a 3rd by self.
so keep 2 , never ever used. to be self sufficient.
this is not a door issue, above 3 lines, its a not getting stranded issue.

no good needs replaced

I locked the 2000 lincoln continental with the key fob but lost it now the ignition key wilolo not unlock the door