How C-rate and run time are calculated
C-rate is current divided by rated capacity. Pulling 50 A from a 100 Ah pack is 0.5C, and 1C by definition is the current that would empty the rated capacity in one hour. Run time is rated capacity times usable depth of discharge divided by current, and recharge time applies charge efficiency on top of that.
Depth of discharge drives cycle life more than anything else. Lithium iron phosphate cells tolerate 80-90% DOD for thousands of cycles, while flooded and AGM lead acid batteries lose cycle life sharply past 50%. Charge efficiency also follows chemistry, roughly 95-99% for lithium and 80-85% for lead acid, which is why a lead acid bank always takes noticeably longer to refill than it took to empty.
Lead acid capacity shrinks as the discharge rate rises, an effect described by the Peukert equation. A battery rated 100 Ah at the 20 hour rate may deliver only 50-60 Ah at a 1C draw, so high rate designs must use the manufacturer discharge curves rather than a simple division. Lithium packs hold capacity far better but still see voltage sag and heating at high rates, so confirm the BMS continuous current limit before finalizing any design.
Frequently Asked Questions
Only at 100% depth of discharge. At 90% DOD it is 1.8 hours, and a lead acid bank will fall short of even that because of Peukert losses. Check the manufacturer discharge curve for the real number.
Some energy is lost to heat and side reactions during charge. Lithium packs also taper into a constant voltage stage near full, where current falls steadily, so a real full charge usually takes 20-30% longer than the calculated value.