Pontoon Boat & Deck Boat Forum

Okay guys and gals,

I brought both my batteries home in November to keep em charged.

One is 2 years old or less and I noticed the sides are kinda sucking in. Is this normal?

The other is less than a year and kinda looks the same but not as bad.

come on guys nothin...?

Well, it has been a few years since I looked at battery designs but I will throw my two cents into the ring. My guess is that the battery has been overcharged. All batteries will produce gas and loose electrolyte as part of normal charging. When properly charged and maintained these losses are minimal over the life of a battery. When a battery is improperly charged the electrolyte loss can be much higher. In a standard battery you can add distilled water to replace the electrolyte that has been lost.

A gel cell is a type of maintenance free battery and is sealed as part of the maintenance free design. The electrolyte is in a jelly as part of that design. It is designed to minimize gassing and electrolyte loss. There is a relief valve built into the case that will vent when the case pressure gets high enough. This is usually caused by overcharging or overheating. When the relief valve operates that gas/vapor is lost and cannot be replaced. The relief valve closes and when the battery cools the case goes on a vacuum. If this cycle of overcharging/overheating is repeated and the relief valve has a good seal this could result in a "sucked in" case.

Often a charger for gel cells is set to a slightly lower voltage to prevent overcharging and loss of electrolyte. Check your charger and see if it is recommended for gel cells. Also check with the battery manufacturer to see what they recommend.

Anyone else got any thoughts on this?

Thanks Wed,

actually I looked on their website and found this.

Case Flexing - Sonnenschein Batteries.

This flexing of the casing walls generally indicates normal functioning of the battery.
It is the process of internal recombination of the hydrogen and oxygen back into water
which gives the very low gassing feature of the cells; This makes unnecessary, the
"topping up" with water which conventional batteries require.

The process is achieved by the use of a pressure valve in each cell which completely seals
against contamination of the cells by external air etc.

The valves act as safety devices against high internal pressure development but allow a
max. working pressure of approximately 0.1 bar to develop within the cells, as internal
gasses recombine.

This slight pressure can cause a slight bulging of the certain battery casing walls.

Conversely, during deep discharge or when the battery is not in use, slight self discharge
and chemical reaction inside the cells can result in a negative pressure - since the valves
will not allow pressure to equalise from outside. This often results in a normal "sucking in"
or contraction of the casing walls .


So it is normal.

Oh well, They said it so much better than I did.

Yes, it is normal but it represents loss of electrolyte and a shortened battery life compared to a properly maintained flooded cell battery. But, since most of us don't maintain batteries properly it is a moot point.

Happy tooning in the new year.

Do you guys use a Battery Tender over the winter. I use one for the Boat battery and one on my Harley. I would never go with out one again. I am no expert but I do know that keeping a full charge is important to the longevity of your battery.

I had just a regular charger. Now I have one though.

No, don't have one yet. Haven't had the boat very long and just got finished with new boat shed & have not got it outfitted yet. I will be getting a maintenance charger soon. I charged both batteries several weeks back and hope that will work until I can get back to charge them again in a few weeks.

I am not sure about gel cells, but dry cells need to be rapidly charged. Trickle charging will fry a dry cell.

What exactly is a dry cell, I know about Gell cell and the AGM wich is Glass Matt. But I am not Familar with dry cell technology. Does anyone have any info on this type of battery.