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 datalogger (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.