The Generators Maintenance: Starter Batteries

Starter Batteries

Why a paragraph dedicated only to starter batteries? Simple: because if they are carefully maintained and safe, the gen set won’t start!

At best, the diesel engine could be equipped with a compressed air starting which is a special optional that we shall deal with in another section.

The starter batteries on the market are now of varying type and they are differentiated by brands, models and characteristics.

To simplify the discussion, I’ll focus on two basic categories : the sealed type and the unsealed one, more commonly defined in the operators’ jargon “with caps” and “without caps”.

The so-called sealed batteries don’t give the possibility of controlling the level of electrolyte liquid in the individual elements except for some of the most recent generations that have a small spy on the top cover which will present a colour change in relation to the internal liquid decay.

So you can use all the external visual and electrical controls as to whether the battery is about to die or it is still holding the charge well.

Firstly and after having properly disconnected the static battery charger in the panel, you have to disconnect the two terminals at the battery poles and , with your tester you should measure the no load charge voltage . In this rest condition the voltage must not fall below the minimum value indicated by the manufacturer  and, in any case not under 12V.

You can also use a specific tool that executes the  download and upload process  and that prints you a small report with the performance data.


Now you can clean the two poles of the battery well and reconnect the terminals starting with the positive then the negative without exaggerating too much when screwing the clamping bolt. Fixing must be done in a way the pole is well tight so that it cannot move however be careful to not  damage the clamp or the pole. These latter are very soft.

You can also use a spray  (easily available on the market) which creates a protective film on the pole. After having replenished the charger, now you can measure the voltage at the poles and the absorption to the wires of the same power supply with a current clamp to make sure that it remains within the required limits and when the correct voltage is reached, it works correctly, gradually reducing the charging current.

But now let’s get back to our above mentioned batteries. The ones “with caps”. You will find one at each item and you should open them not before having worn gloves, goggles and protective masks. The electrolyte liquid can be brought back to the level by adding distilled water, sold specifically for top-up of the starter batteries. You can also use a convenient semi-automatic top-up like the one in the figure below, which autonomously stops when the liquid is level. However, if you don’t have one, and you  are refilling  with a small funnel, then the two side lines on the battery body indicating the liquid levels MIN and MAX will help you. A key thing that you MUST know is that you MUSTN’T top up a battery with new acid, but EXCLUSIVELY with distilled water otherwise the risk that the new acid rapidly impacts with the charged electrodes generating an explosion is high.

I also recommend  your not filling the battery if the opening of the caps is clear that the elements are completely dry. this is an indication of poor maintenance, a charge too high by the charger or a battery problem.

The elements that are dry and kept in charge can be overheated and have created "gases" which, in contact with the distilled water that you are going to add, can trigger dangerous reactions.