HMMM make sure all wiring os correct guages use correct trerminals from battery ensure both battery earths go back to three points on vehicle EG block chasis battery negative
two grnds on VSR battery and block
use a Circuit breaker and fusible Diode 100amp Break out Boxes on both Battery Postive
,ake sure Alternator is High Amperage
Use shortest distance between cable runs and loads to avoid voltage drops
If using Home Batteries make sure they are designed for this circuit ( need More Info on Battery Type eg AGM wet Maintenance free ect ) usefullinfo for your knowledge and KNOW i do not work for them but found this very Helpfull
kickass they have video tutourials and training on all of this setup
https://www.youtube.com/watch?v=Z9c1hVXBggk Any help please ask im in Melb
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Cheers
Wazza