Lead-acid technology (rechargeable)


AGM and VRLA type leakproof lead-acid rechargeable battery with gas recombination operating principles


Battery type:

Nominal capacity C20:

The present Operating Principles must be strictly observed. The rechargeable battery use instructions have to be displayed in a prominent place near the batteries. Only authorised individuals may service the rechargeable batteries.



The rechargeable batteries are supplied charged. Do not connect opposite poles due to large short circuit currents.


A flammable gas may be discharged from the safety valve if overcharged. Discharge static electricity from clothes by touching an earthed element.


Use isolated tools designed for use with electrical devices. Do not drop and do not touch rechargeable battery poles with metal items. Before commencing works, remove metal clothing elements and other items such as: watches, rings, chains, etc.

Failure to observe the present Operating Principles, attempts to carry out repairs by an unauthorised person or unauthorised changes to the system invalidate the guarantee.


Store rechargeable batteries in a dry, cool and clean place. Storage time is limited. In order to ensure correct operation after a storage period, the following storage conditions should be ensured:


Storage timeStorage temperature
6 months20OC
4 months30OC
2 months40OC

Once the specified time has elapsed, perform a maintenance charge in accordance with the CHARGING section of the present manual.

Voltage measurement in the rechargeable battery’s open circuit may indicate its state of charge. A regenerative recharge is suggested if voltage dips below 2.07V per cell. Failure to observe this condition may result in a significant decrease in the capacity and lifetime of the stored rechargeable battery. It is recommended to make and keep records containing information about the date and duration of every performed regenerative recharge. Such records should be presented in the event of a possible guarantee claim.


Install rechargeable batteries in a clean and dry place. Under normal rechargeable battery operating conditions no gasses are discharged – they may be used within premises with other electrical devices.


Avoid locating and operating the rechargeable batteries in places where elevated or extremely low temperatures occur or in direct sunlight. The difference between ambient temperature and the temperature between given cells should not exceed 3oC. For best lifetime and performance use in the 15oC to 25oC temperature range.

Attention: Operation and storage of partially discharged or completely discharged rechargeable batteries in temperatures below 0°C may result in the electrolyte freezing and the housing to crack which in turn might cause the rechargeable battery to lose capacity.


In normal conditions gas discharge is negligible and natural ventilation is sufficient to cool the cells and remove the effects of an unforeseen overcharge. Provide appropriate ventilation if rechargeable batteries are installed in closed cabinets.


Before start-up all cells have to be checked for mechanical damage, correct polarisation and whether the connections have been correctly made. Electrical connector screws for rechargeable battery terminals should be tightened with a torque wrench compliant with the PN-EN 1090-2 standard.

Ensure the charging device off and no load is connected, then connect the battery to the direct current system. Make sure the terminals are connected correctly. Turn on the charging device and adjust the voltage according to the guidelines below.



Maintenance charging voltage:


2.35 V/cell0oC
2.33 V/cell10oC
2.27 V/cell20oC (references)
2.25 V/cell25oC
2.23 V/cell35oC

Recommended maintenance charging voltage: 2.27 V/cell at 20oC. If the ambient temperature differs by +/-5oC, select maintenance voltage according to the table. On account of the gas recombination phenomenon, a difference of +/-2% in the voltage of given cells may occur. Nevertheless, the total rechargeable battery voltage should be within the tolerance bracket specified above.


VRLA rechargeable batteries should only be operated together with a device ensuring stabilised constant voltage and a limited charge current. To ensure the longest possible lifetime, the charge current should be limited to 10% of 20-hour capacity (0.1C20 [A]). Maximum value of initial charge current specified by rechargeable battery manufacturers is 20% of the rechargeable battery’s 20-hour capacity (0.2C20 [A]).


Equalising charging is required after a deep discharge and/or insufficient charging. This can be performed with a maximum voltage of 2.40 V/cell for a 24 hour period (a maximum of 4 – 5 times a year). The charge current should not exceed 10% of the battery’s 20-hour capacity.  If the battery temperature exceeds 45oC stop charging or temporarily switch to maintenance charging to lower the temperature.


Unacceptable charge current variable components may cause damage and decrease lifetime. It is recommended for charge current variable components to be reduced to 0.1 C20 (in amperes) or ≤1% of the nominal voltage.



The state of charge may be determined on the basis of a measurement taken on the rechargeable battery’s open terminals after a 24h no-use period.


State of chargeVoltage
100%2.15 V/cell
80%2.09 V/cell
60%2.06 V/cell
40%2.02 V/cell
20%1.97 V/cell



Lower voltage thresholds below which further rechargeable battery drain is not permitted are shown below.


1.65 V/cellup to 1h
1.70 V/cellup to 5h
1.75 V/cellup to 8h
1.80 V/cellup to 10-20h


VRLA rechargeable batteries cannot remain in a discharged state and maintenance charging has to be applied immediately. Failure to observe this guideline may result in a loss of the available capacity and a reduced rechargeable battery lifetime.


Under complete rechargeable battery discharge, the sulphuric acid is totally consumed and only water remains in the electrolyte. This results in sulfation of battery plates, which significantly increases internal resistance and the rechargeable battery irreversibly capacity. Rechargeable battery operation or storage in such a state at temperatures below 0° C may cause the electrolyte to freeze and the housing to crack. A completely discharged rechargeable battery should be charged with 2.27 V per cell with current absolutely not exceeding 0.1 C20 in order to avoid excessive overheating. The minimum charging time is 96 hours.

Attention: every incident which results in a complete discharge of a rechargeable battery significantly impacts its lifetime.



VRLA rechargeable batteries are leakproof lead-acid batteries. Electrolyte top-ups are not required. The housing and cover should be dry and dust free. Clean only using a cotton cloth.

During system handover and after expiry of the operational lifetime specified in the Guarantee terms, voltage and maintenance charge current in every parallel branch, voltage and internal resistance of every rechargeable battery in the system should be measured. A capacity test should also be performed under discharge down to the lower voltage threshold. The measured values, discharge tests and power interruptions should be recorded in a log book. Records of the performed measurements and tests should be presented in the event of potential complaints of batteries.


In any situation where VRLA batteries are used for special applications such as cyclical operation or in extremely difficult ambient conditions, it is recommended to contact Wamtechnik for advice.

ZE 02 valid from 23/02/2015