Due to large selection of Li-ion chargers on the market, it seems reasonable to use a Li-ion charger to charge a supercapacitor. A Li-ion charge profile is show in Figure 2-6.

Figure 2-6 Li-ion Charge Profile

To prevent damage and increase battery lifetime, Li-ion battery pack protectors prevent the cells from being discharged below approximately 2.5 V cell. If the pack protector is open due to deeply discharged cells or there is no storage element at the BAT pin, the BAT voltage is <= 2.0 V (VBAT_SHORTZ) and the charger provides a small trickle charge in the 100 mA range to slowly raise the pack cell voltage. Then the charger must charge at a low pre-charge current in the 100 mA to 800 mA range until the battery reaches 2.6-3.0 V typically (VBAT_LOWV). After those two stages, the CC and CV stages are the same for supercap charging as previously discussed. Li-ion batteries are recommended to have charge termination and not be continuously topped off, for example, not be recharged until the battery discharges by a nominal amount (at least 200 mV). Supercapacitors typically do not need trickle charge or pre-charge, do not require charge termination and can be constantly topped off. Luckily, most chargers allow termination to be disabled. But only a few Li-ion chargers allow trickle charge to be disabled. Therefore, some modification from default settings and/or additional circuitry is required for a Li-ion battery charger to charge a supercap.