The Yutong E10's from the video posted by Geoff have a battery life to operate 170KM per day so I decided to do a few calculations.

Service 57 is approximate an 8 mile journey between Newcastle and Wardley via Q.E. Hospital "Quoting Google Maps" which equates to 12.8748 Kilometres.

170 divided by 12 = 14 meaning the E10 could do 7 round trips on the 57 per day on a single charge.

For the 49 from Gateshead to Winlaton via Blaydon & MetroCentre is approximately 13 Mile journey meaning the E10 could do again around 7 round trips per day on a single charge.

I do think the 49 is top contender for the new order of Yutongs as it will release the Euro 6 Streetlites onto other services such as 6/12/12A/33N or 57 thus allowing the Citaros to be withdrawn.