A battery is an electrical storage device. Batteries do not make electricity, they store it, just as a water tank stores water for future use. As chemicals in the battery change, electrical energy is stored or released. In rechargeable batteries, this process can be repeated many times. Batteries are not 100% efficient – some energy is lost as heat and chemical reactions when charging and discharging

Battery Types

Lead-acid batteries

It consists of lead-acid which is very cheap and seen mostly in cars and vehicles to power the lighting systems in it. These are more preferable in the products where the size/space and weight doesn’t matter. These comes with the nominal voltage starting 2V to24V and most commonly seen as 2V, 6V, 12V and 24V batteries. It has Power density of 7 Wh/Kg.

Ni-Cd batteries

These batteries are made of Nickel and Cadmium chemical composition. Though these are very rarely used, these are very cheap and their discharge rate is very low when compared to NiMH batteries. These are available in all standard sizes like AA, AAA, C and rectangular shapes. The nominal voltage is 1.2V, often connected together in a set of 3 which gives 3.6V. It has Power density of 60 Wh/Kg.

Ni-MH batteries

The Nickel – Metal Hydride batteries are much preferable than Ni-Cad batteries because of their lower environmental impact. Its nominal voltage is 1.25 V which is greater than Ni-Cad batteries. It has less nominal voltage than alkaline batteries and they are good replacement due to its availability and less environmental impact. The power density of Ni-MH batteries is 100 Wh/Kg.

Li-ion batteries

These are made up of Lithium metal and are latest in rechargeable technology. As these are compact in size they can be used in most of the portable applications which need high power specifications. These are the best rechargeable batteries available. These have a nominal voltage of 3.7V (most commonly we have 3.6V and 7.2V) and have various ranges of power capacity (starting from 100s of mAh to 1000s of mAh). Even the C-rating ranges from 1C to 10C and Power density of Li-ion batteries is 126 Wh/Kg.

Li-Po batteries

These are also called as Lithium Ion polymer rechargeable batteries because it uses high conductivity polymer gel/polymers electrolyte instead of liquid electrolyte. These come under the Li-ion technology. These are a bit costly. But the battery is very highly protected when compared to the Li-ion batteries. It has Power density of 185 Wh/Kg.

Battery Cut-off Voltage, Minimum Voltage, Charging Voltage

Battery Cut-off Voltage

Different batteries have different cut-off voltage. Cut-off voltage means batteries should never charge more than this volt

Battery Minimum voltage

For longest life, batteries should stay in the green zone means Voltage must Not Exceed Than maximum Voltage and must  not be Less Than Minimum Voltage but continual discharges to those levels will shorten battery life considerably. It is important to realize that voltage measurements are only approximate. The best determination is to measure the specific gravity, but in many batteries this is difficult or impossible.

You can follow the following Battery Voltage chart for different Types of Batteries

Battery Voltage Chart

Battery Charging Current

The charging rate depends very much on the battery’s chemistry – Lead-acid, Ni-Cad, NiMh, Lithium-ion, etc.

The maximum charge rate for wet cell lead acid battery is about 10% To 15% of the amp hour rating and 30% for Lithium-ion batteries. Suppose you have 12v 120 Ah battery (assuming it’s lead-acid) should be charged at 12 to 24 Amps max.

Maximum Charging Current Is always Written on the Branded Batteries(Follow Those Instructions). You can follow the following chart for charging current and charging time calculation for different types of batteries.

Battery Charging Time Formula

Below is a simple battery charging current and battery charging time formulas with a solved example of 120Ah lead acid battery.

Here is the formula of charging time of a lead acid battery.


Charging time of battery = Battery Ah / Charging Current


T = Ah / A



T = Time hrs.

Ah = Ampere Hour rating of battery

A = Current in Amperes


Example based on a 120 Ah battery (This information is available on the label of the battery on the top side)

First of all, we will calculate the charging current for 120 Ah battery. As we know that charging current should be 10% of the Ah rating of the 12v battery. This is because a higher rate may cause the battery acid to boil.

So charging current for 120Ah Battery = 120 x (10/100) = 12 Amperes  Suppose we took 10 Amp for charging purpose, then charging time for 120Ah battery = 120 / 10 = 12Hrs. 

but this was an ideal case…

Practically, it is noted that  20%-40% of losses (in case of battery charging). we suppose 20% loss
then 120 x (20 / 100) = 24 …..(120Ah x 20% of losses)
therefore,  120 + 24 = 144 Ah ( 120 Ah + Losses)
Now Charging Time of battery = Ah/Charging Current
144 / 10 = 14 Hrs ( in real case)

Therefore, a 120Ah battery would take 14 Hrs for completely charging ( with 10A charging current).

Follow The Following chart for battery charging time calculation formula

battery charging time formula