Charging of batteries

Charging the various battery types is easiest and safest with those chargers which are normally supplied with the equipment containing the batteries.

Sometimes you have to choose or recommend a charger for a given battery system. The criteria applied in selecting the charging system is usually:

• Desired time for recharging the batteries, require the shortest time possible or would the standard 12-24 hours be enough?
• Cyclic use or stand-by / parallel use?
• Financially, how much can the charger cost?
• Charging from electricity network or from the voltage source, for example the vehicle or both parts?
• Opportunities for monitoring and alarm for malfunctions?

The different chemical systems have completely different systems and principles for charging and chargers for example, lead-acid batteries can not be used for NiMH . In addition to the fact that the batteries can be destroyed, it is a security risk, for example the risk of fire or explosion.

Tricks and tips

NiCd and NiMH-batteries – not charging full capacity

New NiCd and NiMH batteries, or those which have been some time in stock do not provide full capacity after the first charge, they are also usually more or less exhausted when you buy them (except NiMH cells of Low Self Discharge type, LSD cells ). This is not because of quality problems, but lies in the battery’s chemical “nature”.

• This is sometimes misunderstood, and the customer goes back to the place of purchase to return their battery. Here’s how you can get the battery going again in the best and fastest way:
• Charge the first time at least 16-24 hours, even if the charger indicates “fully charged” after a shorter time.
• Use the battery until it is empty, the unit switches off, etc.
• Now make a new charge according to the charger’s manual, after 2-4 times the battery should give full capacity and you get the best life.

Dont discharge the battery too much

Many of us know that one should discharge the battery (NiCd and to some extent NiMH) before you recharge again, but not seldom do they discharge out “too much”. One should discharge to about 1 V / cell, for example, 4V for a 4-cell battery that is nominally for 4.8V. Thereafter must the load be removed, the easiest way to do this is by discharging with, for example, a phone or device in use, or alternatively with a charger with a discharge function. If one otherwise applies a load in the form of lighting or resistance, and forgets about it, the battery will be destroyed.

Lead and lithium-ion – avoid battery discharge

Lead and lithium-ion need not and should not be discharged unnecessarily, applies in particular to deep discharges. A lead acid battery is destroyed (sulfation on the plates) relatively quickly if left empty.

These types of batteries can advantageously be recharged before they are completely exhausted, unlike NiCd / NiMH. They should not be left with the charger connected unnecessarily long time after full charge with the exception of lead-acid batteries that are specifically intended for stand-by operation.

The battery seems “dead”

The protection circuit in lithium-ion batteries prevents among other things, deep discharge but if you still have “crossed the line” the charger will try to charge the battery again, but it will take longer than normal.

Sometimes this is misunderstood; the battery seems “dead”. Note that this does not have to do with the charger’s capacity, but the protection circuit inside the battery has just done its job.

Lagra med 50-60 procent SOC

Lithium-ion / LiFe cells and batteries are shipped and stocked typically with about 50% SOC (State of Charge). One achieves then the best possible lifespan and the cells are degrade very little internally purely chemically. If you want to store a Li-Ion / LiFe system for longer, 3-6 months or more, you should therefore make sure that you have around 50-60% SOC before putting away the battery.

Extend the battery life

During operation and use one wants obviously to get as much as possible of the battery’s capacity and charge up therefore usually the system as well as discharge to the limits.

However, one can assume that the total life of a battery system gets longer if you do not use the entire capacity of each work cycle.

In some contexts and in larger and with more expensive systems one often has advanced control of charging and discharging level. One dimensions the system to some excess capacity and thereafter uses the range between for example, 20 and 80% of the battery’s total capacity (60% DOD, Depth Of Charge) and can achieve around 8000 cycles, while 80% DOD with the same battery might give around 1500 cycles.

State of charge (SOC) of lead or Li-ion batteries

The voltage measurement can roughly determine the state of charge for a lead acid battery. Applies to 12V (6 cells) batteries at 20 ° C, the battery must have been at rest for at least three hours after charging. Divide or multiplied by voltage values for different numbers of cells.

The charging status of lithium-ion cells can be determined in a similar manner, the table shows the voltage per cell, multiplied by the voltage of the number of cells that the battery contains in the case of higher voltage, for example, by 4 for a battery with 14.4V nominal voltage, etc:

Laddningsstatus för Litium-Jon celler (3,6-3,7V nominell cellspänning) kan fastställas på motsvarande sätt. Observera att de olika delkemierna för Litiumceller ger något olika mätvärden, rådgör alltid med Celltech för din aktuella applikation.