An implantable 
medical device, such as an implantable 
pulse generator (IPG) used with a 
spinal cord stimulation (SCS) 
system, includes a rechargeable lithiumion battery having an 
anode electrode with a substrate made substantially from 
titanium. Such battery construction allows the rechargeable battery to be discharged down to zero volts without damage to the battery. The implantable 
medical device includes battery charging and protection circuitry that controls the charging of the battery so as to assure its reliable and 
safe operation. A multi-rate charge 
algorithm is employed that minimizes charging time while ensuring the 
battery cell is safely charged. 
Fast charging occurs at 
safer lower battery voltages (e.g., 
battery voltage above about 2.5 V), and slower charging occurs when the battery nears full charge higher battery voltages (e.g., above about 4.0 V). When potentially less-than-safe very low voltages are encountered (e.g., less than 2.5 V), then very slow (
trickle) charging occurs to bring the 
battery voltage back up to the 
safer voltage levels where more rapid charging can safely occur. The battery charging and protection circuitry also continuously monitors the 
battery voltage and current. If the battery operates outside of a predetermined range of 
voltage or current, the battery protection circuitry disconnects the battery from the particular fault, i.e. charging circuitry or load circuits.