@IDEngineer,
It took a few years before the penny dropped that the13.8v float charging voltage per 12v SLA
wasn't the optimum voltage level to maintain SLAs at a relentless 365 days a year for years at a time (at least as far as end users were concerned). It undoubtedly was for APC and other manufacturers in that it allowed the use of undersized and expensive SLA battery packs by maximising the energy storage capacity when brand new and for the first year (or two at most) of their service life before going into a decline over the next year or three if you were very lucky or waited until they eventually failed the UPS's weekly battery test cycle.
I'd bought that SmartUPS2000 sans battery box at the Blackpool radioham rally some 15 to 20 years ago (the exact date is now lost in the mists of time) which allowed me the freedom to choose whatever capacity of battery I could afford to buy.
I think I started off with a set of four 7AH SLAs supplementing them with a set of 25AH SLAs purchased the following year at the next rally. At some point, I'd managed to cut a deal with a local car parts/salvage dealer for a set of four NOS 36AH SLIs to build the battery capacity to a grand total of 75AH (based on an unwarranted assumption that the two banks of 7AH and the one bank of 25AH, along with those four SLIs I'd managed to blag for a mere 60 quid still had their specified capacity). A test run with some 300W of loading resulted in almost 6 hours of autonomy before the voltage dropped to the cut out point at 40.4v.
The SLAs survived this 13.8v abuse for maybe a couple of years of service but the SLIs only lasted a mere 6 months which was to me a surprising result considering the much easier life compared to their normal use as SLI batteries. It took another set of 36AH SLIs and remembering the similarly short life of a 40AH SLI I'd used with a CB radio powerpack to increase the peak current output back in the late 80s / early 90s before I realised that SLIs were simply unsuited to this task.
By the time I'd realised the high battery maintenance costs, even when I was paying only a fraction of the full retail price, I'd already gone through two sets of SLIs, one set of 25AH SLAs and a box of sixteen NOS 7AH SLAs I'd purchased very cheaply from my son's best friend plus the first two sets I'd started off with. Mind you, I'd used at least two of the 7AH batteries to replenish the pack in that SmartUPS700 I've given the sack to and at least half a dozen used by the UPSonic 600 (likewise long since retired) which burned through them three or six at a time (36v in one or two banks).
At one point, I had a total of five UPSes in service burning a total of 72W in maintainance consumption (32W for the SmartUPS2000, 20W for the SmartUPS700, 18W for the UPSonic600, 7W on an ancient Emerson30 (my very first UPS which was a modified sinewave type) plus maybe another 8 W on a now forgetable UPS I managed to burn out by connecting it to an external 25AH 24v battery to replace its knackered internal 4.5AH SLAs. This was replaced with an APC BackUPS500 (which uses just a single 7AH SLA) about ten years ago.
As a result of my experience and research, I've now dropped the per 12v battery float charge voltage down to 13.5v[1] on the two remaining UPSes (SmartUPS2000 and the BackUPS500 which uses just under 3W of maintainance for its 350W/500VA's worth of protection) and stopped wasting money on cheap NOS car batteries. I'd made this decision some three or four years ago when I'd had to replace the single 7AH SLA in the BackUPS500 around the time I gave up satisfying the SmartUPS2000's appetite for eating battery packs by removing it from service as a 'protected supply'. It was only due to the purchase of the Parkside inverter genset that motivated me to invest in a set of four 7AH SLAs so I could verify my hypothesis that an inverter genset would solve the problems I'd experienced with a conventional 2.8KVA PowerCraft generator a few years earlier.
The SmartUPS2000 original battery pack is specified to be 18AH so the set of four 7AH SLAs won't offer much autonomy, just enough to run the inverter genset test and provide 5 or 10 minutes on the current 300W load. Recently, I discovered the charm of LFP battery technology which blows away the ancient SLA in regard of every aspect (2000 and more charge/discharge cycle ratings for a 20% loss of capacity when cycled to an 80% DoD and a much flatter discharge voltage curve - improved WH capacity and round trip efficiency compared to even a lightly stressed SLA battery pack limited to 50% or less DoD).
The only thing not to like is their capital cost. If you purchase from any of the UK suppliers, you can land up paying two to three times what you can buy them for when using the likes of Alibaba to purchase them directly from the manufacturers in China.
Four LFP cells in series conveniently creates a 12.8v battery replacement for the classic 12.6v SLA. You just have to size them so their 1C discharge rating matches the peak current demand by the UPS. In my case, I'd need to build a 16s 50AH battery pack for my SmartUPS2000 which, at UK prices, would be an 800 quid or more investment plus carriage charges. Even at 400 quid delivered from the Chinese manufacturer via the auspices of Alibaba, it's still a large investment although it works out at less than the price of two sets of APC branded 18AH battery packs which, rather obscenely imo, are regarded as a 'consumable'
Who the hell stood still for this particular scam?
The LFP battery makes for a one time only capital investment that's likely to outlive the UPS, totally turning the concept of the battery being a 'consumable' versus the one time investment in the UPS itself which now becomes 'the consumable'. An LFP battery pack replacement is more than worthy of consideration. I'll be investigating the pros and cons of ordering a set via Alibaba. So far it's mostly pro and little to no con but I'm not quite ready to pull the trigger on placing an order for a 16 cell 50AH LFP battery pack just yet.
[Note 1] This was a decision backed up by the fact that a secondhand 12AH SLA I'd purchased at our local flea market (which turned out to be 11.95v rather than the 12.5v reading on a borrowed DMM I'd used to assess whether it would be worth its asking price) for just a fiver over five years ago now, had only ever been charged from a pair of 1.2Wpk output solar panels hung outside of the office window for a week or so each summer and then left to rest until the following summer's annual refreshing charge for the first five years of ownership and showing a resting voltage that never dropped below the 12.7v mark.
I use it on infrequent occasions as a test battery. One time I even used it to jump start a 1.6litre automatic with a totally knackered battery that had left me stranded outside of our local chippy one winter's night. What this had demonstrated was that a quality made SLA did not need to be cossetted with a battery conditioning charger to avoid the overhyped sulphation risk. It seemed to me that if the resting voltage could be kept above the 12.7 volt mark, this was sufficient to protect against the sulphation risk, suggesting that an unremitting 13.8V float charge voltage was way more than was good.
The reduced float charging voltage may knock some 5 to 10 percent off the usable capacity but the elimination of the corrosive wear and tear from float charging an SLA at 2.3v per cell makes such a small sacrifice of performance more than worthwhile.
John