If Daly City would allow Muni to add wires at the bus loop for BART, the buses could hook up to recharge while waiting there. And they might have to - my recollection is that the trolley bus aux. batteries are designed for short distances - a few blocks, maybe up to a mile at most. BART is what - a mile (counting out-of-direction travel and time stopped at signals) from the end of the 14 line now?

Really, if the 14R gets to BART, why bother? And note that in SF these days "diesel" bus means, usually, hybrid Tier-4 diesel-electric with emissions approximating what a good CNG unit does.