APC CS 500 UPS Battery Fix

Introduction: APC CS 500 UPS Battery Fix

There are a lot of myths, procedures and tests done on sealed lead acid batteries for recovering purpose. I wanted to have my own experiment and publish it's findings. The test subject was an APC CS500 ups that was not holding a charge anymore and was throwing overload errors or battery error. Knowing that the ups was kind of old the next logical step was to replace the battery, but first it became my experimentation patient.

Why a lead (sealed) acid battery dies:

- Normal wear, life cycle end.

- Over discharged storage which leads to irreversible sulfatation.

- Overheating and electrolyte venting.

The batteries that are used in UPS's are sealed lead acid batteries that are spill proof. Instead of having liquid acid in them they have a paste or a gel which acts as electrolyte. During it's usage the battery is subjected sometimes to high heat environment which sometimes leads to a partial vent of electrolyte. If the battery vents enough electrolyte the internal paste will dry out and will stop conducting electricity rendering the battery completely useless.

To try to recover the battery, you need to open it's sealed cover, remove the one way vent caps and add a small amount of distilled water (deionized). Before doing this you must visually check the battery for cracks or swellings, if either is present then DO NOT ADD WATER and just replace the battery. Also the amount of water should be enough not to drip out of the battery when it's turned upside down.

You will also need a battery charger as the UPS will probably not recharge the battery after the water has been added. A fixed 13.8 Volt low current 500mA -1Amp charger should be used.

The rest of the details are on the video.

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    6 years ago

    Many times the effects of sulfation won't be visible on the outer surface of the battery. Trying to recover these batteries is usually not a productive exercise. The amp hour rating will be a fraction of the original and therefore not acceptable for power backup uses (or any uses).


    6 years ago

    1) A lot of the cheaper APC UPS units kill batteries, it's almost part of the business plan :) Over charge 'em, give 'em a "test" drain as often as possible,chip away at the battery life, and then you have to replace it.

    2) Your comment on cracks or swelling is right. I kept an 12v 7.5Ah ex-UPS battery that had lost capacity (age), and there was "slight" swelling. Then one day, just sitting there -- not even in use, a loud CRACK, and the case had split. If the case is not as smooth and flat as it was when new, recycle it.