I think there's a kit out there, usually marketed towards the RV/ 4x4 custom crowd. Single unit that keps either battery charged, automatically switches over. Something like that anyways. Carl 77rocco 89fox -- Email LIST problems to: scirocco-l-probs@scirocco.org. To unsubscibe send "unsubscribe scirocco-l" in the message to majordomo@scirocco.org