Warning Low battery

[lmanoli86]

Hi

I bought a Renault Megane 1.5 DCI and with 20 minutes the Warning Low Battery comes up on the dash

I have had both the battery and the alternator checked and everything was ok- someone suggested it may be the battery in my key card, so Iv replaced the battery and had a new key done and the light still comes up after about 20 minutes or so.

Also, a lovely new little message that just came up 'check injectors'???

Any help would be greatly appreciated, as am at a bit of a loss.

Cheers