For 2006 V8V, is it safe to use one of those portable battery jump starter packs to start it from the battery directly? The reason I ask is that my battery may be really low and the pack won't detect it when connected to the points under the bonnet. Alternatively, it can detect using a DC-connector to the 12V in the 'ashtray' but I don't think that has the amperage to handle the 'boost' for a jump start.

How long can your cars last before the battery dies - assuming in once instance i) no BDS engaged and ii) BDS engaged?