The largest cause of early failure of lead acid batteries – and therefore loss of warranty on them – is overtopping or undertopping them!
Not only is topping up one of the biggest problems with using batteries but it is also one of the most common reasons battery companies will not honour a warranty. Also, fork lift truck users who complain about the performance of batteries are often not topping them up properly – and they have no idea that when it comes to topping up batteries, too little can be just as bad as too much.
The problem with undertopping is that it increases the acid strength within a battery which increases the corrosion rates on the plates. Low water levels create sulphation at the top of the plates which can then harden and reduce the capacity of the cells.
Conversely, overtopping can reduce the strength of the acid, therefore diminishing the performance of the battery.
During a battery’s discharge and recharge cycle, natural tidal flow occurs within the battery. This means when the battery is discharged to 80 per cent the electrolyte level is at its lowest. When the battery is then charged the level rises to its highest. And during the gassing phase air bubbles chemically produced by the overcharge increase the volume of the electrolyte, raising the level even higher.
If batteries are topped up to the correct level before being charged and then put on charge this will cause the level to rise and when gassing occurs electrolyte will escape and spill across the top of the battery and inside the battery case. This is why it is absolutely the wrong thing to do to top up a battery before it is charged. Also, it is important to remember that when properly charged the battery should only be topped up to a maximum of 5mm above the separators.
Any resulting overspill can also create corrosion and voltage leakage across the battery, reducing the capability of the battery’s capacity. And the corrosion caused by overtopping a battery can leak on to the floor and create potentially serious health hazards.
Finally, because a battery is a chemical product, dissolved metallic solids in normal tap water can cause short circuiting within the cell, causing the battery to run warm and again reducing its capacity. Also, the parts per million of dissolved solids varies hugely across the UK water supply (from 60ppm to 660ppm), which is why it is essential to use deionised and demineralised water when topping up.
So knowing when and how to top up is vital if users want to get the absolute maximum performance and working life out of a battery.