Statistically 80% of all genset “fail to starts” are due to the condition of the DC starting batteries.

Keeping your batteries and charger in good condition will ensure that the genset does start when you need it. A lead-acid battery is just a collection of cells containing lead anode and cathode plates immersed in sulphuric acid creating a potential difference. The movement of lead, oxygen and sulphate ions determines the “charge” of the battery, a battery charger then reverses the electrical discharge of the plates.

AJ Power will supply the majority of their gensets with “dry charged” batteries to overseas customers (mostly due to carriage regulations on acid) and “wet” batteries to domestic customers. A wet battery is already charged and ready to commission when received, a dry charged battery requires a certain procedure to commission and ensure battery service life.

a) Only commission a dry battery when it is needed,

b) Inspect the battery for exterior damage before filling,

c) Remove the sealing plugs, tape or foil,

d) Remove and keep the vent plugs and terminal covers,

e) Use battery grade dilute sulphuric acid with specific gravity 1.270-1.280 at 25 degrees C conforming to BS3031 or better, do not use acid from old batteries.

f) The temperature of the battery and the acid should be in the range of 15-30 degrees C.

g) After taking the necessary Health and Safety precautions, fill each cell with the acid to a level of 8-15mm above the top of each plate, fill each cell one after another and complete the filling in one operation.

h) Leave the battery for 20-30 minutes and then measure open circuit voltage, charge the battery if it is below 12.50V.

i) Refit the vent plug and terminal covers.

j) Wash the battery with hot water and dry it.


Under normal conditions batteries can be installed after filling but an activating charge is recommended, it is essential that a conditioning charge be given in the following circumstances;

1. The battery has not been fitted with 24 hours of filling and activating

2. The specific gravity has fallen below 1.260, measured at 15 degrees C (SG decreases with a rise in temperature, and increases with a fall)

3. The battery does not produce its full capacity due to low external temperatures or unfavourable storage conditions.

Remember that a charging battery vents explosive hydrogen gas and may spill corrosive Sulphuric acid.

Before fitting

Check correct polarity – there have been instances where the polarity on the posts is reversed. Check the DC voltage required by the engine/control system – 2no. 12Vdc batteries supplied can be connected in series for 24v or parallel for 12Vdc, 4no. batteries incorrectly connected can supply up to 48 Vdc!


Securely attached the battery to the baseframe or tray provided, ensuring not to overtighten the clamps, or short the battery terminals with any clamping system.

Ensure the control panel is switched off and the emergency stop button is depressed.

Connect the positive lead first, secure the clamp and cover with the protective boot on the lead, attached the negative lead and repeat.

Power up the DC circuit on the genset and ensure the starting, DC voltage measurement and operation of the battery charger circuit (if fitted).


Always keep the battery top and terminals clean, coat terminals and connections sparingly with petroleum jelly.

Regularly check the electrolyte is not below the minimum or above the maximum levels, only top up with distilled or chemically pure water.

Regularly check the operation of the battery charger, the battery charge fuse/MCB and wiring.


The condition of a Lead Acid battery cannot be determined by measuring the voltage across the terminals or internal resistance alone, a stress test (short circuit test) must be carried out. Fast charging/high current charging of a battery will shorten its usable life. The AJ Power smart trickle charger switches off once the genset starts to allow the engine DC charger to take over, prolonging the life of the battery.

If a battery needs replaced over the lifetime of the genset, ensure that a similar battery with Ah and CCA Starting Current specification is fitted. Also be aware that there are environmental regulations in different countries governing the disposal of lead-acid batteries.

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