For Cummins 6.7 ISB, use AGM Group 31 batteries with 900+ CCA. Duracell (East Penn) and NAPA Legend are both excellent choices with good warranty. Replace both batteries together. AGM handles diesel starting demands better than flooded.
Battery Boost connects house batteries to chassis battery for starting assist - this is normal function. A battery that struggles in cold weather likely needs replacement or has parasitic drain. Test and maintain both battery systems before trips.
Keep your RV comfortable in any weather with this AC, furnace, and heat pump troubleshooting guide.
Store lithium batteries indoors above 32F at 40-60% charge. Wisconsin basement temperatures (55-65F) are ideal. Never charge lithium batteries below freezing - this permanently damages cells. Check voltage every 2-3 months during storage.