Have a 99 chrysler t&c. The engine seems to be in good shape an starts reliably if the battery is not dead, even at 10f below. The problem is that every once in a while the battery looses the charge for an unknown reason . The car turns over slowly and the solenoid chatters in and out. Happens several times a month; I’ve started carrying a spare battery with a fair amount of reserve capacity and 4 ga. cables. Even then, it is iffy as to whether the car will start. It cranks slowly and the solenoid may still drop out.
This has happened even over a short period of time such a s grocery shopping.
I researched one of those lithium battery packs that can be inserted into the cigarette lighter. My understanding is that the emergency pack has to recharge the main battery for some time. It makes sense that you don’t want to run starting current through the aux. voltage outlet.
Should I be letting the spare battery recharge the main battery for a few or more minutes?