What is the Depth Of Discharge (DOD)

 DOD refers to the percentage that the capacity discharged account for the nominal capacity of the battery.

Reducing the DOD can greatly prolong the service life of storage battery.

Overcharging and over discharging will shorten the service life of the battery.

What problem will occur when mix use batteries of different capacities and different voltages?

 When mix use batteries of different capacities and different voltages, leakage or short circuit may occur. These problems occurred because some of the batteries will be over charged and some others are not charged to full capacity. When these batteries are discharged together, the batteries with full capacity cannot be fully discharged while the other batteries with low capacity will be over discharged. In this way, the batteries will be damaged and leakage or short circuit low (zero) voltage will occur.

What is the electrochemical theory for NiMH battery?

NiMH battery use Ni Oxid (NiOH) as positive electrode, hydrogen storage alloy powder as negative electrode, lye (mainly KOH) as electrolyte. When charging the NiMH battery, reaction on the positive electrode:

Ni(OH)2 –e + OH- → NiOOH + H2O

Reaction on the negative electrode:

MHn + ne → M + n/2H2

When discharging the NiMH battery, reaction on the positive electrode:

NiOOH + H2O + e → Ni(OH)2 + OH-

Reaction on the negative electrode: M + n/2H2 → MHn + ne

Overall reaction: Ni（OH）2+MH NiOOH+M+H2O

What are the advantages of NiMH batteries?

1.  Low cost.

2.    Excellent fast charging characteristics.

3.  Long cycle life.

4.  No memory effect. No pollution.

5.  Wide applicable temperature range.

6.  Excellent safety characteristics.

What are the possible reasons for zero voltage or low voltage?

 A)   When batteries are short circuit from outside or over discharged/over charged or charge reverse.

B)    When battery is continuously charged with high current, the electrode swells so that the two electrodes contact directly, short circuit is caused.

C)    Batteries are short circuit or slightly short circuit from inside. Ex. There is spur on positive electrode or negative electrode, which gets through the insulator causing short circuit; Positive electrode and negative electrode are placed inappropriately and electrodes contact each other, causing short circuit; Positive electrodes contact directly with steel case, causing short circuit; Powder on negative electrode drops into the insulator or insulator fails to work well so that positive plates contact negative plates, causing short circuit.

What is penetration test?

 After the battery is fully charged, penetrate the battery from the center of it with a nail Ф2.5mm-5mm and let it stay inside, the battery should not explode or got fire.

What is Temperature Rising Test?

 Charge the battery to full capacity and put it into the oven, increasing the temperature every 5 minutes until the temperature of the oven inside reaches 150c, keep 150C for 10 minutes, the battery should not explode or got fire.

What is Temperature Cycling Test?

 Temperature Cycling Test includes 27 cycles.  Every cycle includes the following steps:

1.       Take the battery from normal room temperature environment into the environment with 66+-3c, 15+_5% and rest for one hour.

2.       Transfer the environment to be 33+_3c 905%, rest the battery for one hour.

3.       Transfer the environment to be 403% rest the battery for one hour.

4.       Rest the battery for 0.5 hour under 25C.

The above four steps make up a whole cycle. After 27 cycles, the battery should not leak, be rusted or have other abnormal results.

What are the advantages of NiMH batteries?

 1.  Low cost.

2.    Excellent fast charging characteristics.

3.  Long cycle life.

4.  No memory effect. No pollution.

5.  Wide applicable temperature range.

6.  Excellent safety characteristics.

How over discharge affect battery characteristics?

 After the battery has been fully discharged and voltage lowers to the designated value, if we continue to discharge the battery, the battery will be over discharged.  We usually set the cut-off voltage according to the discharging current.

We often set cut-off voltage as 1.0V/cell for battery with 0.2C~3C discharge current and 0.8V/cell for 5C or 10C discharge current. Over discharging batteries, especially with large current, can bring disastrous results; over discharging batteries once and again will cause even worse result.

Generally speaking, over discharging will cause battery’s internal pressure to rise, damage activity of positive electrode and negative electrode substance, decreasing battery’s capacity.

What are the possible reasons for zero voltage or low voltage?

 A)       When batteries are short circuit from outside or over discharged/over charged or charge reverse.

B)        When battery is continuously charged with high current, the electrode swells so that the two electrodes contact directly, short circuit is caused.

C)       Batteries are short circuit or slightly short circuit from inside. Ex. There is spur on positive electrode or negative electrode, which gets through the insulator causing short circuit; Positive electrode and negative electrode are placed inappropriately and electrodes contact each other, causing short circuit; Positive electrodes contact directly with steel case, causing short circuit; Powder on negative electrode drops into the insulator or insulator fails to work well so that positive plates contact negative plates, causing short circuit.

What is penetration test?

 After the battery is fully charged, penetrate the battery from the center of it with a nail Ф2.5mm-5mm and let it stay inside, the battery should not explode or got fire.

What are the main characteristics for lithium polymer rechargeable batteries?

 Main characteristics for lithium polymer batteries include voltage, internal impedance, capacity, internal voltage, self-discharge rate, cycling life, sealing characteristics, safety characteristics, storage characteristics, outer appearance, over charge resistance capability, over discharge resistance, welding capability, resistance to corrosion etc.

The lithium polymer battery characteristics testing items:

         Discharging characteristics

         High temperature characteristics

         Low temperature characteristics

         Self-discharge characteristics

         Cycling life

         Internal short circuit test

         Continuous charging test

         Over charging

         High current charging

What are the usual charging ways for batteries?

 1. Charge with constant current:

The charging current is invariant when charging. This is the most frequently used charging way.

2. Charge with constant voltage

The charging voltage is invariant when charging while the inside current of the battery decreases as the voltage of the cell rises.

3.Charge battery with constant current (CC) first. When the voltage of the cell rises to a designated value, keep the voltage of the cell unchanged, charge the battery with constant voltage (CV), the charging current decreases until to zero.

The 1^st and 2cd charging ways are usually applied for NiMH, NiCd batteries and the 3^rd charging ways are for lithium polymer batteries.

Designation for Lithium Polymer Battery:

 The designation is made up of 3 parts:

Ex.: L503562 3.7V 1000mAh

Spec: T: 5.0mm, W: 35mm, L: 62mm, lowest capacity: 1000mAh,

Ex: L503562 3.7V 1100mAh

Spec T: 5.0mm, W: 35mm, L: 62mm, lowest capacity: 1100mAh.