The key not the fobon my 2002sebring has a battery. how do I change it?

https://www.thoughtco.com/replace-the-battery-in-your-cars-keyless-remote-281715
https://www.farmandfleet.com/blog/how-to-replace-your-key-fob-battery/
https://www.wikihow.com/Change-a-Mercedes-Key-Battery
https://www.myalexandertoyota.com/blog/how-to-change-the-battery-in-your-toyotas-key-fob/
https://www.smarthondadesmoines.com/replace-honda-key-battery.htm

See this site for possible solution:
How to reprogram Peugeot 207 car key after changing plip battery Yahoo...

How to reprogram Peugeot 207 car key after changing plip battery Yahoo...

You will preobably have to go to a dealer and have the key codes re-registered.

So you changed the battery in the key? and this is the problem i suspect that you have lost the chip out of the key when you took the key apart to change the battery ,dont worry its happens to the best of us the phone rings or you get distracted -if you have lost the chip then try the spare key if you do not have one call the dealer and have a spare key and a new chip in your key programmed up-

hold the key fob in your hand.
hit the key extend button.
the back side of the key should pop off with some help from the area the key is at when retracted
the battery # CR2032
hope this helps

There is a special procedure involved in keying your fob to your car once the battery has been changed. You must lock and open the door with your key. Turn the ignition to "on"(not start) then push the fob's open and close button, then shut off ignition. This procedure is done everything the key battery is changed. Hope this can help you!
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Motorcycle Diagnostic Scanner

Hello. Great question.

Yes, the battery can be the culprit, and it is easily changed.

Remove the metal key from the side of the smart key, and then split the casing of the smart key, via the slot. There is a small circular battery that you can remove and replace. Use the exact same battery.

No Re-programming is necessary. The smart key frequency is coded to the car. Changing the battery does not change the frequency.

Thanks for such a good question.

If you have the diamond shape key, the battery is not replacable. If you have the square shaped key, the battery is replacable, but that is obvious because of the screws on the back of the remote.if you have the diamond shape key, it is recharged when its inserted into the ignition. If the key hasn't failed, taking a long trip 60 min. or longer should recharge the battery. If there is no change in the operation of the key after your long trip, most likely the key has failed and needs replacement.

sounds like you have either a problem with your selenoid or your starter. try shorting the selenoid, if the car cranks then replace it, if not then it's the starter. I should say that the first thing to do is make sure that the battery wires at the starter aren't corroded and are tight, make sure power is getting to the starter, most systems have an in-line fuse, this could be gone.