So what if I just used a cheap car battery with thick wires in place of the UPS battery? Are you saying that the battery would die pretty fast or faster than a lead or calcium battery would? I'd like to just get the cheapest battery I can that will take the 220w load of my server (said by UPS utility) for say an hour, the longer the better but if a good quality battery will make a noticeable difference or last longer then I might look into one.
EDIT: Also, what do you think of these?
http://www.bgmicro.com/index.asp?PageAction=VIEWCATS&Category=298 (thinking the last or second to last) Would a couple of those in parallel do better than my stock battery?
Massive TL;DR coming up again.
Well, the batteries in the link are probably smaller than the stock ones in your UPS, I'm afraid. Most UPSes in that class use two 7 or 12Ah batteries in series, so that wouldn't offer much improvement. You could hook them up in parallel, but then the problem is the same as last time; They would get discharged at different rates.
You should first of all open up and check what batteries there are in the UPS, so you're sure you get the right voltage when you buy new ones. If there are two batteries, you have to get two batteries.
To offer any kind of improvement in runtime, you should look into 17-18Ah batteries if the ones in your UPS are 7Ah, and a bit over 20Ah (22-28) if there are 12Ahs in it.
If the load from your server is 220W, and you want an hour of runtime, it's quite easy to figure out what you need. If we take it that the UPS is 85% effective (pretty typical for home ones) at that load, we get a power draw of 253W from the batteries. That means you will need at least 253Wh of power in your batteries, or 21Ah in a 12V configuration. However, this is where the tricky part comes in. You see, lead-acid batteries of all kinds are less effective when discharged rapidly. In a one-hour discharge cycle, you'll only get about 50-60% of the actual capacity of the battery, and to make it even more confusing, you never, ever use 100% of the capacity. UPSes usually go down to about 75% before shutting down. A 20Ah battery becomes something in the lines of 9-10Ah usable power, and your current (likely) 7Ah ones are something laughable.
So, even if you theoretically only need around 20Ah, what you will have to buy is closer to 50Ah. But don't panic, this isn't as horrible as it sounds, as your UPS with quite high certainty is running on 24V, you don't need to get some 50Ah beasts, as Watts (Or capacity)=Current*Voltage, you can split it up into two batteries. On top of that, the lower current draw is much lighter on the batteries, so you can get more efficiency out of your batteries, perhaps around 70%, in which case, two 17Ahs could suffice pretty well.
As for different kinds of batteries, about every battery you use in a UPS is lead-acid, but there are many different kinds. There are normal starter batteries, like those found in cars, non-spillable gel batteries, like those in UPSes, calcium, silver... The list could go on forever. There are basically four kinds that you are interested in:
Standard batteries: The ones with caps that you find in cars. They're pretty cheap, can work pretty good in a UPS, and if kept charged can last over a decade. These are, however, designed to give massive currents for a short amount of time, rather than the fairly little one delivered for an extended period of time in a UPS, and thus get quite a low efficiency (Around 55% for one hour of discharge). These are also not very good at handling deep-cycles. 10-20 cycles (I.e, running the UPS on battery until it shuts off from low battery voltage) could ruin them and steal more than half of their capacity. They're cheap, simple, not very safe (Quite easy to spill acid if you tilt it) These can be found in any well-sorted car accessory shop.
Calcium-enhanced batteries and/or marine/golf cart/deep-cycle batteries: These are the kind of batteries I prefer. They're still fairly cheap, come in all sorts of capacity, and are generous with the deep-cycles; They can often take closer to 50 cycles before dropping in capacity, many even several hundred, and in most cases have several enhancements to improve deep-cycle- and short-term discharge performance, often hitting 70% in a one-hour discharge cycle. These usually don't have any caps on top, but instead a small chamber with a catalyst to re-combine any hydrogen gas emitted with the electrolyte, making them 100% maintenance-free, and very hard to spill. Can be found in boat shops, off-road shops and well-sorted car shops.
SLA (Sealed Lead-Acid) batteries: These are the kind currently in your UPS, and in the link you posted. These are about the most expensive lead-acid batteries you can find, but they have very strong advantages and disadvantages. The largest ones tend to be 17-30Ah, and they can reach up to 80% efficiency in quick discharge cycles, and virtually take no harm from deep-cycles at all, most being able to take 200+ without damage. They're virtually indestructible (trust me
), and more or less 100% safe to use. You can't spill them, you can drop them, you can hit them with a hammer, and they just work. They should make tanks out of them. Really. The disadvantages are short and clear: 1. They cost. The $:Ah you pay is ridiculous. 2. They're short-lived. Five years is the average life span, compared to 12-15 for the ones above. 3. They don't come big. If you want something that lasts during long outages, you can't get one big, you gotta get 50 small.
Motorcycle batteries: These are usually of type 1 or 3 mentioned above, and come in sizes between 4 and 20Ah. They could be something you're looking for, as two 17Ah ones in series would give you pretty much backup time, as long as you think a little about the power draw.
