This table provides a comparison of battery technologies.
Type
Nominal voltage [V]
Specific energy[MJ/kg]
Energy density[MJ/L]
Specific power[W/kg]
Charge/discharge efficiency [%]
Energy/consumer-price [kJ/US$]
Self-discharge rate per month [%]
Cycle durability
Zinc–carbonacid dry cell
1.5

0 very good

1
Alkaline
1.5

0 good 1
Lithium
3
1.0
2.1

0 low 1
1
Lead–acid
2
0.108 – 0.144
0.216 – 0.270
180
50 – 92
25.2(sld) – 64.8(fld)
3 – 20
500 – 800
LiFePO4
3.2

0.79
300

4.5
2000 – 7500[1]
LiPo
3.7
0.36 – 0.95
0.90 – 2.23
10000

5.0
1000
Lithium-ion
3.7
0.36 – 0.95
0.90 – 2.23
~250 – ~340
80 – 90
9
8
400 – 1200
Low self-discharge NiMH
1.2
0.2 – 0.4
0.5 – 1.1
250 – 1000

9.9
0.9 [2] – 3.7
500 – 1800
Nickel–iron

0.108 – 0.180
0.108
100
65 – 80
5.40 – 23.76
20 – 30
>5000
Nickel–metal hydride
1.2
0.216 – 0.432
0.504 – 1.08
250 – 1000
66
9.9
30
500 – 1000

Traditional rechargeable batteries have to be charged before their first use; newer low self-discharge NiMH batteries hold their charge for many months, and are typically charged at the factory to about 70% of their rated capacity before shipping.

Grid energy storage applications use rechargeable batteries for load leveling, where they store electric energy for use during peak load periods, and for renewable energy uses, such as storing power generated from photovoltaic arrays during the day to be used at night. By charging batteries during periods of low demand and returning energy to the grid during periods of high electrical demand, load-leveling helps eliminate the need for expensive peaking power plants and helps amortize the cost of generators over more hours of operation.

Battery charging and discharging rates are often discussed by referencing a "C" rate of current. The C rate is that which would theoretically fully charge or discharge the battery in one hour. For example, trickle charging might be performed at C/20 (or a "20 hour" rate), while typical charging and discharging may occur at C/2 (two hours for full capacity). The available capacity of electrochemical cells varies depending on the discharge rate. Some energy is lost in the internal resistance of cell components (plates, electrolyte, interconnections), and the rate of discharge is limited by the speed at which chemicals in the cell can move about.

Battery manufacturers' technical notes often refer to voltage per cell (VPC) for the individual cells that make up the battery. For example, to charge a 12 V lead-acid battery (containing 6 cells of 2 V each) at 2.3 VPC requires a voltage of 13.8 V across the battery's terminals.

Damage from cell reversal[edit]
Subjecting a discharged cell to a current in the direction which tends to discharge it further, rather than charge it, is called reverse charging. Generally, pushing current through a discharged cell in this way causes undesirable and irreversible chemical reactions to occur, resulting in permanent damage to the cell. Reverse charging can occur under a number of circumstances, the two most common being:
When a battery or cell is connected to a charging circuit the wrong way around.
When a battery made of several cells connected in series is deeply discharged.
In the latter case, the problem occurs due to the different cells in a battery having slightly different capacities. When one cell reaches discharge level ahead of the rest, the remaining cells will force the current through the discharged cell. This is known as "cell reversal". Many battery-operated devices have a low-voltage cutoff that prevents deep discharges from occurring that might cause cell reversal.
Cell reversal can occur to a weakly charged cell even before it is fully discharged. If the battery drain current is high enough, the cell's internal resistance can create a resistive voltage drop that is greater than the cell's forward emf. This results in the reversal of the cell's polarity while the current is flowing.[3][4] The higher the required discharge rate of a battery, the