Pod warning ??

[Mr.t]

Needed to disconnect the battery at the weekend, to complete my stereo install. All went well, then went out for a run, no problems at all. Stopped at the pub for a swift one, well it was hot !!, got back in the car started up no problem, ran sweet as a nut, but now have the following warning come up on the pod -

!WARNING!
.0 volts

...anyone know what this means. Drove back home, around 75 miles, with the warning still staring at me, but the car didn't miss a beat. Can anyone help/advise ?. Thanks