hello people, please help,

I have a 1990 fiesta rs turbo. when i have fired her up and shes idling over she is just a little lumpy, then when i turn the lights on she sounds a little drained, then when i turn my main beam on she sometimes cuts out,
This sometime happens when driving, tho she doesnt cut out just sounds really drained as if shes gonna go!!

I have checked the battery and its charged up fine, i also checked the connections to the battery and they r fine also. The alternator was reconditioned about 10-12 weeks ago so this should be fine too.

Please help