The term C-rate refers to the rate of charge or discharge of any battery, expressed in relation to the battery’s capacity. A C/10 rate on a 220 amp-hour battery string would be 22 amps (220 ÷ 10); a C/20 rate would be 11 A (220 ÷ 20). For long service, batteries must be charged at a C-rate sufficient to overcome internal resistance under varied conditions and age. As a general rule, flooded lead-acid batteries need at least a C/20 rate to charge and equalize properly. A C/7 charge rate is about the highest that these batteries can tolerate.