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Home Frequently Asked Questions Replacing UPS Batteries Can I put larger batteries in my UPS?

Can I put larger batteries in my UPS?

UPS equipment is typically designed to operate for up to 5 minutes at full load, which doesn't sound like a lot of time but in reality that should be plenty of time to save your work and shut down your computer safely. Many people are looking for a longer UPS runtime however and that is what we will discuss here.

Physical Size

Obviously the first restraint is the physical size of the UPS and its capacity to hold larger batteries. The battery capacity of a UPS is closely related to the VA rating, but you may note that often UPS of a larger rating are the same physical size as smaller units. For example we will look at the APC SUA750RMI2U and SUA1500RMI2U. As the names suggest they are rated at 750VA and 1500VA respectively. Now we look at the RBC-22 and RBC-24. Both the UPS and the battery cartridge are the same physical size. In this instance there is certainly room for larger battery.

The first place to look and determine if there is a quick and easy solution to increasing your runtime is the user manual for your unit. Check and see if there is a higher rated unit that is the same physical size as yours, then check and see if that is fitted with a higher rated battery. In some cases you will find there is a bracket designed to secure the battery which must be removed however this is usually not difficult, and depending on the changes you may find yourself with incompatible connectors or a shortage of links between the batteries. These are usually easily overcome with a little bit of cable and a crimper.

What if I cant fit them inside the UPS?

If there really is no extra room, or you are looking to put very large batteries on the UPS then they will have to be housed outside. This will mean extending the battery connection cables outside the UPS and it can get a little more difficult. It is best to find a suitable enclosure to house the batteries in rather than having them sitting out in the open. The enclosure should be vented so gases do no accumulate, and the cables should be arranged in such a way that they can not be crushed, cut, or rubbed against a metal edge. If a suitable enclosure cannot be found then ensure that the battery terminals are covered for safety purposes.

A great place to source a suitable UPS battery enclosure is a local electrical wholesaler, they will have a range of large plastic enclosures plus the cable glands you will need to protect the cable.

How much extra runtime will I get from my UPS?

That all comes down to the load connected to your UPS and the size of the batteries. If you need a precise figure, battery manufacturers provide discharge curves for their batteries but their are a couple of basic figures that will give you a guide. The amp-hour rating of a battery is typically its discharge characteristics over 10 hours. This means a 100 amp-hour battery will happily provide 10 amps for 10 hours. It will not however provide 100 amps for 1 hour. A 100 amp-hour battery when discharged at 100 amps will only provide power for about 30 minutes.

So what does this mean for you, well the simple way to look at it is that if you double your battery capacity, you will more than double the run-time available, the increase in run-time is exponential to the increase in battery capacity, so if you are only getting 5 minutes of your 7 amp-hour batteries don't think that you need 70 amp-hour batteries to get 50 minutes.

What about the battery charger in the UPS?

Unfortunately the standard battery charger in the UPS is only designed to charge the standard UPS batteries. That doesn't mean that the charger wont charge larger batteries, but it does mean that it will take longer for the batteries to reach full charge.

Are there any risks in fitting larger UPS batteries?

Yes. Always the most important factor in any endeavour is safety, from a safety aspect it is important to ensure that the terminals are covered and any external cabling is safe from physical damage.

Second is the risk of overheating and damaging the UPS. While larger units feature ventilation fans to help cool the UPS, smaller UPS often only use heat-sinks and rather small ventilation holes in the UPS housing. When you add larger batteries and the power fails, the UPS will be operating in a heat generating mode for longer than it was designed and if the heat is unable to dissipate the UPS could be damaged. When the UPS is recharging larger batteries, as mentioned previously, the charger will be operating for longer a full capacity and there is a risk that this too may overheat and be damaged.

Are there any other options to get longer runtime on my UPS?

The first is to buy a larger UPS, as we said at the start a larger UPS will have larger batteries, so a larger UPS running at 20% load will last longer than a smaller UPS running at 80% load. The second is to look for a UPS that has an external battery connector, that means the manufacturer offers an external battery for extending your runtime, and this is a safer, easier, and often more aesthetically pleasing option.


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