How would you install a switch to use leisure battery as starter if vehicle starter battery has discharged? and you have a split charge relay fitted?
Thanks.
Btw, I tried to access resourses but couldn't open anything.
If you did want to use the Leisure Battery to start the engine, you would need a much thicker cable then usual.
What you can do, if the starter battery is gone a bit low (as opposed to discharged/flat) is use the leisure battery as a bit of an booster.
If you have a Victron Cyrix-CT Battery Combiner (a posh version of a Split Charger Relay), you can fit a simple low-current momentary switch which will turn the combiner/relay on for 30 seconds and during that time try and start the engine.
If you have a switched relay, then it depends how that is switched to if you can use it to connect the batteries together without the engine already running.
If you have a typical Voltage Sensing Relay (VSR), then you can't go through the relay but would have to fit a separate battery isolation switch.
This kind of switch connected in parallel would give you a direct connection between Leisure and Starter batteries when on, and only have a connection via the relay when off
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If you are still to buy a Relay and want this functionality, the small extra cost of the Victron Cyrix is worth it for the quality and convenience of the product (it also has a 5 year warranty).
But all the above is to provide the occasional "damn, left the lights on" kind of situation resolution. If you are looking at this functionality due to an actual regular starting problem, you really want to be fixing the issue at source.