Battery charger is an electronic device which is used to charge batteries. The suitable voltage required to charge the batteries is 2.15V per cell so for 12V battery, 12.9V charger is required. If voltage is less than 12.9V then charging will not take place. However, most of the time, a higher voltage is used because it forces the charging reaction at a higher rate.

The typical charging voltage is between 2.15V to 2.35V. This voltage can be applied to a fully charged voltage without overcharging or damage. But when battery is not fully charged with much higher voltage per cell can be applied without damage i.e. 2.45V/cell.

Batteries are used in two ways -1) Standbymode or 2) Cycling deep charge

  • Standby Batteries – These batteries are used in standby but kept constantly on charge. Batteries are rarely charged. Such batteries should be charged at a float voltage of 2.25 to 2.3V peer cell (or 13.5 V to 13.8V for 12V battery).This low voltage prevents the battery from losing water from long float charging.
  • Cycling deep charge – Batteries those are used in deep discharge cycling mode can be charged up to 2.45V per cell (or 14.7V for 12V battery) to get the highest charge rate as long as the voltage is dropped to the float voltage when the charge is complete.


(Note:-The capacity of charger voltage for lead acid battery should always be higher than the battery discharging voltage.)




Trickle chargingTrickle charging means charging a fully charged battery under no-load at a rate equal to its self-discharge rate, thus enabling the battery to remain at its fully charged level. A battery under continuous float voltage charging is said to be under float-charging.

Float Charging – A float charger (also called a storage charger, maintenance charger, or smart charger) will charge a battery at a similar rate as a battery self-discharges, thus maintaining a full capacity battery.

Difference between Float & Trickle charging – The main difference between a trickle charger and a float charger is that a float charger has circuitry to prevent battery overcharging.


Boost ChargingBoost charging means charging a drained battery which needs high charging voltage and charger will draw high current so that battery is charged in less time. The amount of current can be fixed in the charger.