Frequently Asked Questions
A. There are many different battery 'types' of which Lead Acid & Lithium are the more popular. 'Lead Acid' and 'Lithium' refers to the technology (what's inside) of the battery. For the purpose of this article, we consider 3 different categories of Lead Acid batteries - Flooded/Wet Cell, VRLA & OPzV. Flooded/Wet Cell batteries are more commonly used in cars, automotive vehicles and older stand-alone systems. The acid is in liquid form and in some cases can be seen as 'flooding' over the plates inside a battery, hence the name. VRLA (Valve Regulated Lead Acid) batteries get there name because they are supposedly 'sealed' but this is not entirely true as the battery has valves. Internally, the acid is immobilised and gases that form are recombined. If an excess of pressure arises, this bleeds off through the valve. VRLA batteries come in 2 main types: AGM & Gel. AGM (Absorbent Glass Mat) relates to the type of separator between the lead plates. The acid is absorbed and immobilised in this separator which separates the positive and negative plates. A well-constructed VRLA Gel uses a polyethylene separators, but the electrolyte (liquid inside) between the plates is a of a gel consistency.
A. Power Charge AGM batteries are your typical Absorbent Glass Mat (AGM) separator batteries. Power Charge X-CEL batteries are a higher specified AGM battery with pure lead plates that incorporate 1.6% of tin in the lead. The addition of tin into the plates markedly reduces sulphation and delamination which occur as a result of normal use of the battery. Power Charge GEL batteries incorporate a polyethylene separator and a thixotropic gel which results in superior performance in cyclic and higher temperature applications. Power Charge ENDUROGEL batteries are a premium gel battery with pure lead plates that incorporate 1.6% tin in the lead and also features a Catalyst Life Extender. This catalyst improves the efficiency of the gas recombination resulting in lower loss of gases and, in doing so, has a major beneficial effect on the life & performance of the battery. This range is the battery of choice for heavy cyclic applications, such as mobility scooters and solar energy storage applications. The catalyst also reduces the damaging effects of higher temperatures.
A. The term 'deep cycle' generally refers to a range of batteries capable of releasing charge over a long period of time. Over-against a starter battery, which is used more for starting a motor, where the charge is taken out of the battery for a few seconds and then the battery is immediately recharged. In an application where the battery will be discharged and recharged as in mobility scooter or solar energy storage, it is imperative to use a 'deep cycle' battery technology such as Gel or Lithium.
A. 'Cycle use' refers to cyclic applications where the battery is heavily drawn on to power the device, often in the absence of another external power source. At a later stage the battery is then recharged. Typical examples are solar energy storage systems and mobility scooters. With your solar system, after the sun sets or on a cloudy day, the battery (if specified correctly) will power the device until the sunshine starts recharging it. During winter, absence of charging the battery for several days, referred to as 'solar drought' can place sever stress on a battery. A VRLA AGM battery over-discharged in this way may never recover its capacity while a gel will. 'Standby use' refers to standby applications where the battery is on constant mains powered charge. e.g. most security & fire alarms operate this way. and Uninterruptible Power Supply (UPS's), where the battery is charged all the time and only drawn on very seldom when there is power interruptions.
A. Depending on the application and battery type, different battery instruments are available and a program of REGULAR periodic testing is recommended to ensure and evaluate the Health and State of Charge of the battery. Absence of regular maintenance may mean that, if and when you do have a power failure, there is not enough capacity to maintain a critical operation during an emergency.
Quick Indication: an intelligent battery tester, such as the 612 IBT, is suitable for a quick test. A small unit gives indication of capacity and voltage, and is recommended for smaller UPS and telemetry batteries.
Cyclic Load: for more comprehensive testing, load testing a battery is the recognised way of obtaining a realistic assessment of the residual capacity in a battery. Battery capacity analysers, such as the BACA unit (for batteries 10Ah-70Ah) and CCOLT unit (for for batteries 26Ah-1000Ah), are reliable instruments for this application. A high degree of accuracy is achieved, bit it requires the batteries to be fully charged, then the BACA or CCOLT applied which discharges the battery under test. An extrapolation from the results obtained may be made, giving a very accurate assessment of the capacity of the batteries.
Impedance: an impedance meter, such as the RE856 unit or PITE, allows a quick live circuit test but requires the baseline impedance measurement before the readings may be of any use. This technique is recommended for larger UPS & Solar systems where interruption of the power supply is an issue or an inconvenience. The readings obtained suggest the health of the battery but give no indication of residual capacity.
A. This equation is mostly used for UPS applications and is: W = I x V. e.g. a 12V 9Ah battery would have 108Whs (12 x 9 = 108Whs)
A. NO, VRLA deep cycle batteries do not have a memory! One of the major draw backs of the older battery technologies, such as NiCad's, was that they had a memory and were unable to discharge past the 'remembered' previous discharges. For example, a rechargeable razor: because a user would typically use 15% when shaving and then put the razor on charge until the next time, eventually the battery only had 15% capacity. VRLA batteries do NOT display this feature. On the contrary, smaller low depth discharges and regular charging will result in the most prolonged usable life with VRLA batteries.
A. Batteries are generally rated on 2 factors;
The first factor: 'C' Rating - which is the capacity the battery can deliver over a set amount of hours:
- smaller VRLA batteries are generally rated C20 (20 hours)
- larger VRLA batteries are generally rated C10 (10 hours)
- solar batteries are generally rated at C100 (100 hours - 4 days which relates to the autonomy)
- And the second factor, cut-off voltage - which is the voltage that the battery is discharge to.
A. For example, 12V7Ah C20.
'12V' represents the voltage: so this is a 12V battery
'7Ah' is the indication of capacity. This needs to be read along with the 'C20' next to it, which means that if the battery was discharged at 350mA or 0.35A over 20 hours, your battery will still be viable at the end of this period. It is very important when working with VRLA batteries that the '7Ah' does NOT mean you can drain 7 Amps for one hour. On the contrary, the one hour rate is 3.6 Amps.
A. There are a number of factors that determine the life of a VRLA battery, but the most prevalent ones are:
Sulphation - probably the worst killer. This is the result from either excessive deep discharges and poor charging practices, In an AGM battery, this is irreversible.
Battery Dryout - this is caused by high temperatures and excessive cycling. The battery loses its moisture through the valves and this moisture cannot be replaced.
Battery Self-discharge - if a VRLA battery is inactive and is left in excess of 6 months without being charged, it will start losing its capacity.
Depth of Discharge - the deeper (the more capacity that is be taken out of the battery) the shorter the batteries usable life will be.
A. YES, overcharging does damage batteries - common causes of over charging a battery are:
- the charger is too large for the battery, so it is delivering more current to the battery than it can handle
- you have a faulty charger, or
- there is a faulty battery in a series of batteries or cells
Over charging a battery will accelerate sulphation and battery dryout, which consequently shortens the life of the battery.
A. YES, over discharging does damage batteries. In the VRLA 12V7Ah example above, we have drawn 7Ah over 20 hours, at the end of this discharge the battery is NOT at zero volts but will typically be around 9.5 to 10 volts. Discharging below this voltage is over-discharging the battery and is damaging it! The common cause of over discharging a battery is: the system is drawing more power than what the battery is capable of delivering. In other words, the battery was under-specified. Over discharging a battery will lead to deeper cycles which in turn accelerates the demise of the battery.
A. The first question: how critical is the application. Sometimes lack of power is life threatening and then the battery size needs to be oversized somewhat. Secondly, what is the current drain: how often will this amount of energy be removed from the battery and then how quickly would you need this energy replaced. As we mentioned above, and this is especially important in cyclic and solar energy storage applications, that the battery is sized correctly. If 100% of the capacity of an AGM battery is extracted with each cycle, only 300 cycles may be expected of a typical AGM VRLA battery, whereas that same battery is capable of delivering 30% of its capacity for 800 cycles.
A. This is done by the use of a formula: Battery Ah / (hours to charge/2)
i.e. a 100Ah battery, 8 hours to charge is 100/4 = 25A charger
A. The power that comes from a grid power station and is available at your household power point is called alternating current (AC). Batteries and solar panels produce direct current (DC). In a typical household system of solar panels and batteries, your solar array will produce DC power. This DC power is then converted to AC by the solar inverter, to make it compatible with the AC mains power coming into your house from the grid. A battery system also uses DC. The batteries are usually connected to the AC mains power in a similar way to that used for the solar panels. Thus, an inverter converts DC power from the batteries to AC power. This makes the system suitable for connection to the grid, and allows the batteries to charge and discharge depending on your household usage.
A. Grid connected solar systems use the term kilowatt (kW) to define the output power of a unit.
kilowatt (kW) = Volts (V) x Amps (A)
For example; a 3kW photovoltaic (PV) solar system would have an output of 12.5A at 240VAC
A. kWh refers to the amount of continuous power output you get from a battery storage bank.
kilowatt hour (kWh) = Volts (V) x Ampere hour (Ah)
24V 500Ah = 12kWh (12000Wh's)
A. The formula for calculating the size of the charger required is:
The battery Ah / (hours to charge/2) - i.e. a 100Ah battery with 8 hours to charge is 100/4 = 25A charger.
REMINDER – when the charger light goes GREEN, it doesn't mean the charger is finished, it’s just that the charger has completed the boost charge which takes the battery to around 90% capacity.
A. The C rating is the way the batteries capacity is displayed i.e. 100Ah/C10
The C rating tells you the amount of current you can discharge from the battery over a certain time period (measured in hours). The shorter the time period, the smaller the C rating will be. Hence why a battery rated at C100 has a larger capacity than a battery at C10.
E.g. 2 PCEG 1000 – 2V 1000Ah/C10 or a 2V 1200Ah at C100.
This means that at 10 hours, this battery discharges 1000Ah but over 100 hours, this battery discharges 1200Ah.
The reason behind this is that the battery chemicals can react better at a slower discharge which results in more capacity being extracted from the battery.