I have an online MetaSystem UPS with a failed lead acid battery. The UPS uses four 12V 5Ah batteries in series. My question is whether it is possible to instead of using four 12V batteries, I use only one. I am asking because some electronic circuits have an inbuilt capability to accept a very wide range of voltages.

that will be a single 48V 5Ah battery, are you shure they aren't in parallel?

Yes, I am sure because I opened it to test the battery.

unless the presence of dedicated sensors, then voltage is 48, regardless of the number of batteries, you could also use 30x AAA batteries, but i doubt you'll get 5Ah

Could you provide a link to the product specifications?

I share the concern expressed by gengisdave over whether the batteries are in series or in parallel.

• 48 Volts seems non-standard. 12 Volts tends to be standard.
• What was the result of your test? (in volts)
• Did you test each battery individually? (the batteries must be disconnected from each other.)

Any batteries that you install would need to be rechargeable.

Have you checked with Radio Shack? I have bought replacement batteries at Radio Shack for American Power Conversion UPSs.

There were jumpers connecting the anode of one battery with the cathode of the next battery. So, I am more than certain that the batteries were connected in series for a total voltage of 48 volts. Moreover, from an engineering point of view, a voltage of 48 volts has the advantage of requiring a lower switching current. This means, the parasitic inductances and capacitances would cause less interference from being generated.

Considering what I have just wrote, it seems, I answered my own question.

The number of batteries isn't really important, but the voltage and capacity (Ah) is.

Most (if not all) UPS systems use the battery voltage as an indicator of battery health and capacity. If the voltage is too low during load, the batteries are considered depleted and the UPS shuts down. If it's below a certain threshold while idle, charging is needed. If the voltage is either significantly below the nominal battery voltage, or if the batteries can't be charged at all (very low charging current), the UPS will conclude that the batteries needs to be replaces.

Using batteries with a lower nominal voltage or the same voltage but lower capacity can be quite dangerous. The UPS is likely to significantly overcharge such batteries, which will cause the release of a mixture of hydrogen and oxygen gas. This gas mixture is highly flammable, and the smallest spark could cause an explosion.

I've replaced a lot of UPS batteries over the years, and more often than not a failed battery with one or more shorted cells (which means a drop in nominal voltage and capacity) will have overheated to the point where the plastic has actually melted and the battery will be physically deformed. The removal procedure for such batteries may include the use of a large hammer. Using a battery with a lower nominal voltage may produce the same result. It's not something I would consider doing.

@Steve R.: 48 volts is actually pretty much standard for medium-sized and large UPS systems. Smaller UPSer (700-1500 VA) typically run on 24 volts using two 12 volt batteries in series, although 36 volts is not unheard of (like the 1500 VA PowerWare 5115 model). Only the smallest systems run on 12 volts, and they typically have a single 12 volt battery and a run time of less than 5 minutes.

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Thanks for your very informative reply.

Can I replace the batteries with others having the same voltage and chemistry but a higher capacity? The original capacity was 5Ah, I found a capacity of 8Ah.

As a rule, using batteries with a higher capacity is not a problem.

Of course, if the capacity is drastically higher (say, connecting a 100 Ah battery bank to a UPS designed for 7 Ah batteries), it may take a very long time to charge the batteries to full capacity. It may even be impossible for a small UPS to keep such a large battery bank charged, as the rate of self-discharge could actually exceed the charging capacity of the UPS.

But replacing a 5 Ah battery with an 8 Ah battery of the same voltage should be no problem at all.

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Thanks.

Thanks.