The CR3000 rechargeable lead-acid battery base requires more than 16 Vdc to properly charge the batteries. The DCDC18R Boost Regulator was designed for this purpose. Failure to use the DCDC18R with the lead-acid rechargeable battery base will result in permanently damaged batteries. (The batteries will remain below deep-discharge levels.)
The CR3000 internal lead-acid batteries are used whenever the car battery is too low to power the data logger (less than 11 V). For example, when the engine is turned off or during start-up when the vehicle battery voltage drops due to starter current demands.