I’d like to start off by saying I’ve used STH as a reference for a long time, but this will be my first post. I hope someone can find this valuable, if only as something to laugh at, or as a good warning.
In all honesty, I will however say that while I won’t recommend that anyone do this because of the hazards involved, it did work for me. If you burn down your house as a result of reading this, please don’t say I didn’t warn you that it is an awful idea.
This was a very simple DIY project that does not warrant the amount of text that follows, but I thought I’d add a little bit of history here to tell about the long-term results, anyways. I’ll include a few pictures, but if anyone wants more detailed info, I will be happy to share.
Above: this is how the unit sits now. Note the batteries in marine boxes with the lids securely fastened
At the facility where I recycle batteries, back when the battery dropoff was a trailer that was not access controlled (now you have to drop off all batteries at a counter), people would dump UPS units that had failed batteries, rather than removing them first and taking those. I figured (correctly) that was why most of those units were there. When dropping off car batteries one day, I snagged 2 1400 VA UPSes: an APC and some other brand that I cannot recall. Bot had bad batteries, which I removed and returned to the collection facility later.
Since these were basically free, I decided I would test out a hypothesis that I had at the time: If the battery capacity is increased in a UPS, the charging time would increase, but so would the usable backup time. Both units used multiple sealed lead-acid batteries setup in a 24V configuration. In order to test this, I purchased some battery cables, some connectors, and 2 of the cheapest SLI (note SLI, not deep cycle) automotive batteries that I could find that had decent CCA ratings. My reason at the time was that with the SLI batteries, I would have more run-time than deep-cycle, and that my power outages were infrequent enough that the damage from a very low number of deep-cycles would still not exceed the normal wear and tear in their intended environment (starting cars in all sorts of weather). Where I lived at the time, while we did lose power for hours or more during the winter or summer storms, it was fairly common that power would go off for just a few minutes or less.
To actually use the batteries in the 24V configuration with the UPS, the internal cables needed to be made to connect to the car batteries, and the batteries needed to be connected to one another in series. I don’t have any pictures from the no-name UPS, but I do of the APC. A hole was cut in the side to run the cables to the external batteries, and the sharp edges were covered to prevent cutting of wires and any shorts that would result from that.
In order to allow easy connection to the battery bank, I used some pre-wired automotive battery connectors taken from a golf-cart or electric wheelchair or something of the sort (I forget which, now). If I was going to do this without what I had on hand, I would probably still use pretty much the same thing: https://www.aliexpress.com/item/32977993126.html. This is a battery connector rated at 50A, 600V, identical to the one built into the back of the unit for the battery disconnect (meant to be pulled out when servicing the unit).
Above: APC UPS on its side, showing battery connector used to replace original connectors for internal battery, and matching hole made to allow for external connection.
I setup and tested first with the off-brand unit. One thing that was interesting about it was that it had several 100A fuses in parallel in between its original batteries. I kept that when switching to the SLI automotive batteries, and kept that fuse holder in place when moving over to the APC, later on.
The off-brand unit lasted for about 1.5 years before it appeared that it would no longer convert the 24VDC to 120VAC, even though it would still charge the batteries. I assume this is because I was constantly running the unit right at its capacity, and probably over-taxed it. My first lesson from this experiment: try not to overload UPS’s.
The cables and batteries got switched over to the APC at this point. I was very impressed at how this functioned. With the 1400VA running at right about full load (okay, so maybe I didn’t learn my lesson with the other unit), I would get several hours of run-time, as opposed to the 45 or so minutes that I believe those things normally give out of the box. Of course, as the charging circuit is designed for a much lower capacity, after a long power-outage event, it took a VERY long time to recharge the batteries to full. The batteries that I used for this setup lasted for a little over 7 years, and for that entire time they delivered very well.
Above: old setup. Visible is connection coming from inside of case through hole cut in side vent.
Eventually, something went wrong. I noticed that everything in my rack that was powered by this UPS was shutting off during the unit’s self-test, and was immediately concerned. I looked over at the unit, and to my horror, the floor underneath and in front of the batteries was wet. Apparently, one of the batteries had exploded. I had seen this in cars that I had worked on before (I was a mechanic and auto-tech instructor at the time), but foolishly, it had not occurred to me that this could happen with my UPS. What a mess! Lessons #2 and #3: Don’t use SLI batteries for UPSes (use deep cycle only), and if you use automotive batteries for a UPS, USE A BATTERY BOX!
Above: electrolyte spray and battery that blew its top off
Above: closeup of exploded battery. The vent cap and bits of lid were blown very far away, and the computer directly above this battery had the paint on the underside entirely ruined by the splash of sulfuric acid from below.
Above: stain on floor from battery acid that leaked onto it.
For those interested, here is what I believe happened, and why I believe that it did:
SLI batteries are designed to delivery as much current as possible for a short period of time, but are not designed to be deep-cycled. In order to maximize current delivery, SLI batteries have thinner lead plates that are jammed as close as possible, with PVC separators to prevent them from touching and shorting internally. By using thin plates, the number can be increased, which allows for more surface area for the chemical reactions occurring. These thinner plates are more prone to stress from deep-cycling, but also by being close together, they are more susceptible to crystallization that can form between plates, shorting them out. When these plates become shorted and load is placed on the battery, it generates a tremendous amount of heat, boils the electrolyte mixture, and can eventually ignite the hydrogen and oxygen mixture that is given off in the charging and discharging process and from the boiling of the electrolyte.
Deep-cycle batteries are designed to be drained more fully without taking as much damage, but also may be designed to reduce the likelihood of such internal shorts. Even if this is not the case, I can say with certainty that if I had my batteries in proper boxes, the worst damage that I would have received was a few drips of electrolyte on the wood supporting the batteries within my rack. Instead, the underside of one of my computers was sprayed with a solution that stripped the paint off of it, and the floor underneath the batteries was permanently stained. Also, cleaning up sulfuric acid and an exploded battery was no fun. Again, this would have been much simpler with a proper case, which I started using immediately after, along with deep-cycle batteries that I bought to replace the SLI ones.
TL;DR:
In all honesty, I will however say that while I won’t recommend that anyone do this because of the hazards involved, it did work for me. If you burn down your house as a result of reading this, please don’t say I didn’t warn you that it is an awful idea.
This was a very simple DIY project that does not warrant the amount of text that follows, but I thought I’d add a little bit of history here to tell about the long-term results, anyways. I’ll include a few pictures, but if anyone wants more detailed info, I will be happy to share.
Above: this is how the unit sits now. Note the batteries in marine boxes with the lids securely fastened
At the facility where I recycle batteries, back when the battery dropoff was a trailer that was not access controlled (now you have to drop off all batteries at a counter), people would dump UPS units that had failed batteries, rather than removing them first and taking those. I figured (correctly) that was why most of those units were there. When dropping off car batteries one day, I snagged 2 1400 VA UPSes: an APC and some other brand that I cannot recall. Bot had bad batteries, which I removed and returned to the collection facility later.
Since these were basically free, I decided I would test out a hypothesis that I had at the time: If the battery capacity is increased in a UPS, the charging time would increase, but so would the usable backup time. Both units used multiple sealed lead-acid batteries setup in a 24V configuration. In order to test this, I purchased some battery cables, some connectors, and 2 of the cheapest SLI (note SLI, not deep cycle) automotive batteries that I could find that had decent CCA ratings. My reason at the time was that with the SLI batteries, I would have more run-time than deep-cycle, and that my power outages were infrequent enough that the damage from a very low number of deep-cycles would still not exceed the normal wear and tear in their intended environment (starting cars in all sorts of weather). Where I lived at the time, while we did lose power for hours or more during the winter or summer storms, it was fairly common that power would go off for just a few minutes or less.
To actually use the batteries in the 24V configuration with the UPS, the internal cables needed to be made to connect to the car batteries, and the batteries needed to be connected to one another in series. I don’t have any pictures from the no-name UPS, but I do of the APC. A hole was cut in the side to run the cables to the external batteries, and the sharp edges were covered to prevent cutting of wires and any shorts that would result from that.
In order to allow easy connection to the battery bank, I used some pre-wired automotive battery connectors taken from a golf-cart or electric wheelchair or something of the sort (I forget which, now). If I was going to do this without what I had on hand, I would probably still use pretty much the same thing: https://www.aliexpress.com/item/32977993126.html. This is a battery connector rated at 50A, 600V, identical to the one built into the back of the unit for the battery disconnect (meant to be pulled out when servicing the unit).
Above: APC UPS on its side, showing battery connector used to replace original connectors for internal battery, and matching hole made to allow for external connection.
I setup and tested first with the off-brand unit. One thing that was interesting about it was that it had several 100A fuses in parallel in between its original batteries. I kept that when switching to the SLI automotive batteries, and kept that fuse holder in place when moving over to the APC, later on.
The off-brand unit lasted for about 1.5 years before it appeared that it would no longer convert the 24VDC to 120VAC, even though it would still charge the batteries. I assume this is because I was constantly running the unit right at its capacity, and probably over-taxed it. My first lesson from this experiment: try not to overload UPS’s.
The cables and batteries got switched over to the APC at this point. I was very impressed at how this functioned. With the 1400VA running at right about full load (okay, so maybe I didn’t learn my lesson with the other unit), I would get several hours of run-time, as opposed to the 45 or so minutes that I believe those things normally give out of the box. Of course, as the charging circuit is designed for a much lower capacity, after a long power-outage event, it took a VERY long time to recharge the batteries to full. The batteries that I used for this setup lasted for a little over 7 years, and for that entire time they delivered very well.
Above: old setup. Visible is connection coming from inside of case through hole cut in side vent.
Eventually, something went wrong. I noticed that everything in my rack that was powered by this UPS was shutting off during the unit’s self-test, and was immediately concerned. I looked over at the unit, and to my horror, the floor underneath and in front of the batteries was wet. Apparently, one of the batteries had exploded. I had seen this in cars that I had worked on before (I was a mechanic and auto-tech instructor at the time), but foolishly, it had not occurred to me that this could happen with my UPS. What a mess! Lessons #2 and #3: Don’t use SLI batteries for UPSes (use deep cycle only), and if you use automotive batteries for a UPS, USE A BATTERY BOX!
Above: electrolyte spray and battery that blew its top off
Above: closeup of exploded battery. The vent cap and bits of lid were blown very far away, and the computer directly above this battery had the paint on the underside entirely ruined by the splash of sulfuric acid from below.
Above: stain on floor from battery acid that leaked onto it.
For those interested, here is what I believe happened, and why I believe that it did:
SLI batteries are designed to delivery as much current as possible for a short period of time, but are not designed to be deep-cycled. In order to maximize current delivery, SLI batteries have thinner lead plates that are jammed as close as possible, with PVC separators to prevent them from touching and shorting internally. By using thin plates, the number can be increased, which allows for more surface area for the chemical reactions occurring. These thinner plates are more prone to stress from deep-cycling, but also by being close together, they are more susceptible to crystallization that can form between plates, shorting them out. When these plates become shorted and load is placed on the battery, it generates a tremendous amount of heat, boils the electrolyte mixture, and can eventually ignite the hydrogen and oxygen mixture that is given off in the charging and discharging process and from the boiling of the electrolyte.
Deep-cycle batteries are designed to be drained more fully without taking as much damage, but also may be designed to reduce the likelihood of such internal shorts. Even if this is not the case, I can say with certainty that if I had my batteries in proper boxes, the worst damage that I would have received was a few drips of electrolyte on the wood supporting the batteries within my rack. Instead, the underside of one of my computers was sprayed with a solution that stripped the paint off of it, and the floor underneath the batteries was permanently stained. Also, cleaning up sulfuric acid and an exploded battery was no fun. Again, this would have been much simpler with a proper case, which I started using immediately after, along with deep-cycle batteries that I bought to replace the SLI ones.
TL;DR:
- Yes, you can replace the tiny internal batteries in your UPS with much larger batteries to extend the run-time.
- Make sure to use deep-cycle batteries
- Make sure to use battery boxes, and I would still recommend placing these on top of a tray of some sort if you have nice flooring underneath.
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