Paralleling UPS Batteries

Generally, paralleling the batteries is not a problem. As the other poster pointed out, the charging time will increase. Should you experience a power outage and run the batteries down, it will take longer to get back up to 100% charge, but for most locations with "typical" power quality, this set up would be just fine. One important note on this subject is to not let the batteries drain down to less than 20% charge. These are sealed lead acid batteries and should be thought of as a mini car battery. We all know that if you leave your lights on and drain your car battery more than 6 times in the life of a battery, you permanently affect the lifespan of the battery. Most UPS manufacturers have a setting in the software to set the minimum battery charge percentage.

R. Jessen

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Battery Guy - ReplacementUPSba
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Your UPS uses gel type batteries. DO NOT use liquid acid batteries, such as car batteries for your UPS. The charger for the UPS was designed for a particular type of battery with a specific charge current range. The charging circuits sense the battery load during charge.

With a liquid acid battery, there is a chance of it being over charged, and thus can cause boiling! This is very dangerous. Liquid acid batteries must be used in a well ventilated area. They can easily give off some sulphuric acid fumes which are very corrosive, and they also give off hydrogen gas. This is not a very good situation for indoors. The so-called seal on these batteries are mainly to prevent acid spill if the battery is briefly tilted.

Jerry G.

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Jerry G.

In my experience, the charge current limit for the native batteries is far lower than the larger automotive or marine deep cycle types folks sometimes use as replacements and undercharging is the problem. The VRLA charge profile from the UPS is usually 0.1C to 0.3C during charge below Vmax followed by Vmax constant as trickle charge. The charge controller may shut down when it sees that the battery is not following the VRLA profile if using wet cells also.

Regarding paralleling of batteries, it may be wise to isolate each battery (group of cells) with diodes (of appropriate current capacity) when making parallel connections between batteries of varying age and capacities to prevent internal current loops. Heat sink the diodes if dissipation ratings require.

Using marine deep-cycle batteries with an external charger is sometimes a good strategy for a UPS, especially if the UPS is robust enough for extended runtimes such a strategy would permit.



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