Charging phases of a charger

A charger has two charging phases. A lithium-ion charger starts with constant current: it charges with the maximum current it has available. For a 2 amp charger that is 2 amps. The maximum current is stated on the rating plate of the charger. Once the charger reaches its maximum voltage, it can no longer deliver that maximum current. At that point phase two begins, which is called constant voltage. The charger holds at its maximum voltage and the current drops. When the current falls below 0.3 A the charger stops charging, and on most chargers the LED then turns green.

Differences between chargers

There are many different chargers on the market. They usually differ on the following points.

  • Charging current: The current the charger delivers. A 2A charger charges the battery at 2 amps, which adds 2Ah every hour. In theory a 10Ah battery is then full in 5 hours; because the current drops in the second charging phase, it takes longer in practice.
  • Charging voltage: The maximum voltage, which depends on the type of battery. For example a 24V or a 36V battery.
  • Quality: Chargers come in different qualities, by which we mean the components used inside. A cheap charger is often light. The maker gets there by overstating the maximum current on the label: the charger then charges at only 1 amp instead of the promised 3 amps. We also see components getting very hot because they are too lightly rated for the job. That shortens the life of the charger, and it does nothing for efficiency or safety either.

How the type of charger extends the life of your battery

The life of a lithium-ion battery depends on several factors, one of which is the number of recharges. Research has shown that a battery lasts many times longer when it is not charged all the way up and not discharged all the way down. See the table below. The voltages are per cell: a 36V battery has ten cells in series, so 4.10 V per cell means 41 V for the whole pack.

Charging voltage per cell (V)

Number of recharges before capacity drops to 70%

Usable capacity

4.25

200–350

105–110%

4.20

300–500

100%

4.15

400–700

90–95%

4.10

600–1,000

85–90%

4.05

850–1,500

80–85%

4.00

1,200–2,000

70–75%

3.90

2,400–4,000

60–65%

Source: Battery University

The table shows that a battery lasts longer when it is not charged to full. Most chargers charge to 4.20 V per cell. A charger that stops at 4.10 V almost doubles the number of recharges, and it also lowers the risk of overcharging as the charger wears. The price is range: on each charge you use 10 to 15% less of the capacity. Ask us which of our chargers work this way.