There are two GEL batteries used on a power wheelchair, the display shown 'low battery error' when the voltage goes to 23.5 V, and got back to 26.5 V after just a little while charging, repeatedly.

What can be the problem?

 

Your batteries may be at the end off their life. How old are they?
It is VERY important to never leave SLA batteries in the flat state. That kills them quite rapidly. Have they sat unused for a length of time, particularly being discharged?

If you leave it on charge overnight, does it hold up in use?

 

Your batteries may be at the end off their life. How old are they?
It is VERY important to never leave SLA batteries in the flat state. That kills them quite rapidly. Have they sat unused for a length of time, particularly being discharged?

If you leave it on charge overnight, does it hold up in use?

Yes, they are not been used for few years, but they can be charged up to 11/12 V.

 

I would say you need new batteries. Leaving them flat for so long destroys the surface by building a Sulphate layer up and greatly reduces the capacity. The same thing happens to car batteries as they share a similar chemistry.

 

Sla batteries have a shelf life of 5yrs as long as they are on float, then they start to fail upto 10yrs,, manufacutrers reccomend replacement over this period.

 

They don't last long if they are stored in a flat condition.

 

I would say you need new batteries. Leaving them flat for so long destroys the surface by building a Sulphate layer up and greatly reduces the capacity. The same thing happens to car batteries as they share a similar chemistry.

I'm using smart charger, they said it be able to Desulfate.

 

I'm using smart charger, they said it be able to Desulfate.

Ok. Leave the charger on for a few days and see if it come ok again. If you have a good smart charger, it should be ok to have the wheel chair on charge when it is not in use.

 

they can be charged up to 11/12 V.

A fully-charged gel-cell battery, after resting a few hours after charging, should have a voltage of about 12.7-12.9V.

 

Desulphate rarely if ever works, i wish you luck but don't depend on it working.