1. VRLA technology

VRLA  stands  for  Valve  Regulated  Lead  Acid,  which means   the   batteries   are   sealed.   Gas   will   escape through the safety valves only in case of overcharging or cell failure. VRLA  batteries  have  exceptional  leak  resistance,  and can be used in any position. VRLA batteries are maintenance free for life.

2. Sealed (VRLA) AGM batteries

AGM   stands   for   Absorbent   Glass   Mat.   In   these batteries  the  electrolyte  is  absorbed  into  a  glass-fibre mat   between   the   plates   by   capillary   action.   As explained   in   our   book   ‘Energy   Unlimited’,   AGM batteries  are  more  suitable  for  short-time  delivery  of very high currents (engine starting) than gel batteries.

3. Sealed (VRLA) Gel batteries

4. Low Self-discharge

Because  of  the  use  of  lead  calcium  grids  and  high purity materials,  Victron VRLA batteries can be stored during long periods of time without recharge. The rate of  self-discharge  is  less  than  2%  per  month  at  20°C. The   self   discharge   doubles   for   every   increase   in temperature with 10°C. Victron VRLA batteries can therefore be  stored  during up  to  a  year  without  recharging,  if  kept  under  cool conditions.

5. Exceptional Deep Discharge Recovery

Victron   VRLA   batteries   have   exceptional   discharge recovery, even after deep or prolonged discharge. It  should  however  be  stressed that repetitive deep discharge   and   prolonged   discharge   have   a   very negative  influence  on  the  service  life  of  all  lead  acid batteries, Victron batteries are no exception.

6. Battery discharging characteristics

The  rated  capacity  of  Victron  batteries  refers  to  a  10 hour discharge, in other  words: a  discharge current of 0,1 C. The effective capacity decreases with increasing discharge  current  (see  table  1).  Please  note  that  the capacity  reduction  will  be  even  faster  in  case  of  a constant power load, such as an inverter.

Table 1: Effective capacity as a function of discharge time. (the lowest row gives the maximum allowable 5 seconds discharge current)

Our  AGM  deep  cycle  batteries  have  excellent  high current  performance  and  are  therefore  recommended for high current applications such as engine starting. Due  to  their  construction,  Gel  batteries  have  a  lower effective  capacity  at  high  discharge  currents.  On  the other  hand,  Gel  batteries have  a  longer service  life, both under float and cycling conditions.

7. Effect of temperature on service life

High temperature has a very negative effect on service life. The service life of Victron batteries as a function of temperature is shown in table 2.

Table  2:  Design  service  life  of  Victron  batteries under float service

8. Effect of temperature on capacity

As  is  shown  by  the  graph  below,  capacity  reduces sharply at low temperatures.

9. Cycle life of Victron batteries

Batteries  age  due  to  discharging  and  recharging.  The number  of  cycles  depends  on  the  depth  of  discharge, as is shown in figure 2.

10. Battery  charging  in  case  of  cycle  use:  the  3- step charge characteristic

The most common charge curve used to charge VRLA batteries  in  case  of  cyclic  use  is  the  3-step  charge characteristic,  whereby  a constant  current  phase  (the bulk phase) is followed by two constant voltage phases (absorption and float), see fig. 3.

During the absorption phase the charge voltage is kept at  a  relatively  high  level  in  order  to  fully  recharge  the battery within reasonable time. The third and last phase is  the  float  phase:  the  voltage  is  lowered  to  standby level, sufficient to compensate for self discharge.

Disadvantages    of    the    traditional    3-step    charge characteristic:

:: During   the   bulk   phase   the   current   is   kept   at   a constant and often high level, even after the gassing voltage   (14,34 V   for   a 12 V   battery)   has   been exceeded.  This  can  lead  to  excessive  gas  pressure in  the  battery.  Some  gas  will  escape  trough  the safety valves, reducing service life.

:: Thereafter the absorption voltage is applied during a fixed  period  of  time,  irrespective  of  how  deep  the battery   has   been   discharged  previously.   A   full absorption   period   after   a   shallow   discharge   will overcharge  the  battery,  again  reducing  service  life. (a.  o.  due  to  accelerated  corrosion  of  the  positive plates)

:: Research   has   shown   that   battery   life   can   be increased by decreasing the float voltage to an even lower level when the battery is not in use

11. Battery charging: longer battery life with Victron

4-step adaptive charging Victron  developed  the  adaptive  charge  characteristic. The 4-step adaptive chare curve is the result of years of research and testing. The  Victron  adaptive  charge  curve  solves  the  3  main problems of the 3 step curve:

::  Battery Safe mode

In  order  to  prevent  excessive  gassing,  Victron  has invented  the  ‘Battery  Safe  Mode’.  The  battery  Safe Mode will limit the rate of voltage increase once the gassing  voltage  has  been  reached.  Research  has shown that this will reduce internal gassing to a safe level.

Variable absorption time

Based on the duration of the bulk stage, the charger calculates   how   long   it   will   keep   the   battery   in  absorption.  If  the  bulk  time  is short,  this  means  the battery   was   already   charged   and   the   resulting absorption time will be short. A longer bulk time will also result in a longer absorption time.

Storage mode

After completion of the absorption period the battery should be fully charged, and the voltage is lowered to the  float  or  standby  level.  If  no discharge  occurs during the next 24 hours, the voltage is reduced even further and the battery goes into storage mode. The lower   storage  voltage reduces corrosion of the positive plates. Once every week the charge voltage is increased to the absorption level for a short period to compensate for self discharge (Battery Refresh mode).

12. Battery   charging   in   case   of   standby   use: constant voltage float charging. When  a  battery  is  not  frequently  deeply discharged,  a 2-step charge curve can be used. During the first phase the  battery  is  charged  with  a  limited  current  (the  bulk phase).  Once  a preset voltage  has  been  reached  the battery is kept at that voltage (the float phase). This  charge  method  is  used  for  starter  batteries  in vehicles, and in uninterruptible power supplies (UPS).

13. Optimum   charge   voltage   of   Victron   VRLA batteries. The  recommended  charge  voltage  settings  for  a  12 V battery are shown in the following table.

14. Effect of temperature on charging voltage

The  charge  voltage  should  be  reduced  with  increased temperature.  Temperature  compensation  is  required when the temperature of the battery is expected to be less than 10°C / 50°F or more than 30°C / 85°F during long  periods  of  time.  The  recommended  temperature compensation for Victron VRLA batteries is -4 mV / Cell (-24 mV /°C  for  a  12 V  battery).  The  centre  point  for temperature compensation is 20°C / 70°F.

15. Charge current

The charge current should preferably not exceed 0,2 C (20 A for a 100 Ah battery). The temperature of a battery will increase by more than 10°C if  the  charge  current  exceeds  0,2 C.  Therefore temperature  compensation  is  required  if  the  charge current exceeds 0,2 C.

Other capacities and terminal types: at request

End of discharge voltage: 10,8 V for a 12 V battery