is the energy consumed by the auxiliary devices during operation.
2.1 Commercial battery for Drones
The most important disadvantages of the Ni-Cd are high negative temperature coefficient, memory effects, high self-discharge, limited service life (the performance starts to deteriorate after 200-300 cycles). Heavy load reduces the battery's cycle life. The most important disadvantages of the NiMH configuration is a high self-discharge rate and the fact that, when charged at a very high charge rate, hydrogen formation can lead to cell rupture. Conversely, when deeply discharged, the reverse polarization of the cell can appear, thus causing the capacity reduction of the battery. The most important disadvantages of the Li-ion is that the internal resistance can heat, thus causing failure of the battery. This is why overcurrent and overvoltage systems are needed in order to assure proper operation. Lithium batteries also degrade at high temperatures and serious degradation occurs when the cell is discharged below two volts. Lithium-sulfur batteries typically employ a negative electrode comprised of metallic lithium. If the electrode is not adequately protected by a passivating  layer there could be safety concerns. Lithium sulfur batteries are typically limited to a maximum of 100 charging cycles. The key barrier to commercialization LiFePO4 was intrinsically low electrical conductivity.
 
2.2 Metal-Air Batteries
Batteries of next generation promise to provide a high energy density. They consist of an air cathode, which traps oxygen gas, an electrolyte which may be solid, aqueous, non-aqueous (organic), and a metal anode.  Table 3 shows commercial devices on board UAVs. A summary of advantages and disadvantages of metal-air batteries is given in Table 4. Table 5 shows a comparison of metal air batteries.
Battery type
Anode
Cathode
Electrolyte
Voltage V
Nominal
Capacity
(mAh)
Energy density
Self-discharge
(% month)
Memory effect
Recharge cycles
 
(Wh/Kg)
Wh/l
Ni-Cd
Cd
Ni oxide
Potassium hydroxide
1.2
1100
42
80
10
yes
1500
NiMH
MH
Ni oxide
potassium hydroxide
1.2
2500
100
175
20
yes
1000
Li-ion
C
LixCoO2
lithium salt
4
740
165
300
<10
no
1200
Li-poly
C
LiCoO2 or LiMn2O4
polymer electrolyte
ND
930
156
ND
<10
no
500-1000
Li-S
Li
S
 
2.2
 
1000
1100
 
no
50
LiFePO4
C
LiFePO4
 
3
 
90
183
 
no
2000
Al-ion
Al
graphite
[EMIm]Cl
 
60
 
 
 
no
7500
SC
C
C
 
2.5
 
 
 
 
 
>10^6
 
Table 3: Commercial rechargeable batteries and   supercapacitors (SC) on board UAVs.
 
Advantage
Disadvantage
High energy density
Limited power output
Flat discharge voltage
Reversibility of discharge products
No or small environmental problems
Pore clogging by discharge products
Low cost
Instability of contacting to air
Long shelf life
 
Table 4: Major advantages and disadvantages of metal-air batteries
  Type
 
Open circuit voltage at 25°C/V
Theoretical specific energy density/WhKg-1
O2 mass included
O2 mass excluded
Li/O2
2.96
5.200
11140
Al/O2
2.73
4300
8130
Na/O2
1.94
1677
2260
Mg/O2
2.93
2789
6462
Ca/O2
3.12
2990
4180
Zn/O2
1.65
1090
1350
Si/O2
0.8-1.1(practical),2.2V(theoretical)
5360
8470
Table 5: A comparison of metal air batteries.
The most important disadvantages of Zn/O2 are corrosion between the anode and the electrolyte, low lifetime when they are recharged electronically and formation of dendrites on the anode. The most important disadvantages of Mg/O2 is that the battery discharges quickly. This reduces the efficiency of the battery, because it needs to recharge after a short period of time. This also causes the battery to create heat. Corrosion caused by the electrolyte is another issue with magnesium anodes. It reduces the life of a battery, which makes it less practical. The most important disadvantages of Al/O2 is that it is not rechargeable and that the anode discharges quickly. These two problems also cause the battery to generate heat, which causes water loss in the electrolyte and thus decreases the life of the battery while the battery is idle and while it is discharging.
 
 
2.3 Super-Capacitor Storage Systems
Figure 2 shows a typical carbon double layer supercapacitor cell.