Frequently Asked Question

Replacement batteries

Last Updated 6 years ago
Please consider replacing your batteries if any of the following conditions apply:
  • UPS shows low battery level despite you have charged it for sufficient time
  • UPS shows weak batteries
  • UPS is running for more than 3 years without battery change
  • The backup time is dramatically reduced comparing to the initial performance
  • Regularly performed battery test (scheduled by software) will report issues with batteries
What batteries should you choose to replace old ones?

Naturally the new batteries should have the same technical specification as old ones to ensure full compatibility. The only exception is the most critical parameter - energy capacity given in Amper-hours (Ah), this may be the same, bigger or under some conditions even smaller than existing batteries. If you insist to install batteries of smaller capacity, please consult with us.

Attention: Always replace all batteries inside the UPS at the time, never mix old and new ones. Use only one type of batteries, never install mixed types of batteries.

Battery Capacity (Ah) will directly influence the backup time, but it will remain compatibile with the UPS if other parameters are fulfilled. Please pay attention to the parameters:
  • dimensions must be 99 x 65 x 151 +/-2 mm, equipped with T2 terminal - the battery must fit into the same place
  • Special UPS batteries for deep-discharge application; never use car batteries
  • Nominal voltage: 12VDC; Float charging voltage 13.6-13.8VDC or wider; Cycle use charging voltage 14.5-15.8VDC or wider
  • Maximum continuous discharge current: minimum 40A
  • Maximum charging current: minimum 2A
  • Capacity recommended minimum as the batteries being replaced
  • working temperatures must fit your environment (consider for special desert/arctic applications)
Hint: As it may seem that there are many parameters to check, in fact there is a common industry standard for UPSs and in most cases asking for UPS batteries at your local store will suffice.

You cannot find battery capacity (Ah)? Your new 8Ah offers worse performance than old 7Ah?

Although battery capacity is sometimes the only given parameter, it is fundamentally wrong to use it. Essentially 7Ah means it will provide 0.35A (current) for 20h (total 20h x 0.35A = 7Ah)*. This value is always given in reference to 20h time period, as agreed in industry. It is false to assume it may provide 35A for 0.2h (12min)! In fact, most generic purpose 7Ah batteries will be able to supply around 12A for 12min (not 35A!). Typical UPS application aims to provide power supply for 5-20min in case of a power failure. For all of those reasons battery manufacturers (righteously) stopped providing current capacity. Instead they are referring to "300W/5min" or other more useful data. This became more critical for special "high discharge" batteries. Despite having the same nominal 20h current capacity, they can deliver even 50% more power for shorter periods like 5-10min! Rating by far more critical for UPS application than 20h-rating.

So how to benchmark the batteries?

Well, it is not easy to say what is better: 7A battery, "300W/5min" battery or "10A/15min". Fortunately laborous recalculation is not necessary. You will easily find battery's datasheet online and you can check battery performance in "Constant power discharge in Watts" table.

*More precisely it is 0.35A for 20h for the varying voltage (dropping, with cut off at 9.6VDC). This is also misleading data, because as voltage is dropping, the power is not constant, while most of the application would rather require relation watt in time, instead of ampers in time.

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