I was recently given a few old APC UPS devices because the batteries in them were toast. devices appear to be from about 93-94, tested off pair of 2 6V batts in series and inverter seems ok. don't relly think its worth replacing batteries for like 20$ per battery. the devices are 1 smart ups V/S 650 and 2 back ups 400. considering running at least the big one if not all three off an old 760CCA truck battery that's just waiting to be recycled anyways because had trouble cranking truck.
not sure how well ups charger would maintain a battery that size, but if it got too low just pull the battery and use a normal charger.
also not sure if charging batty would make a noticeable amount of gas that could be bad. saw something similar somebody did, but not sure how much hydrogen this would make, and if be a bad ide to have in a house. wouldn't think would make very much especially the small charge made by UPS charging.
also not sure if over charging or running to long could make battery fail and leak. if becomes sulfated or something won't be big deal old battery anyways.

 

Truck batteries are not ideal for powering a ups. They are designed to provide a high current in a short period of time as opposed to working over a long period of time,wich you would want in a ups battery.

You would be better to buy a battery for a ups.

 

I might interested in taking one of those off you hands.

 

Truck batteries are not ideal for powering a ups. They are designed to provide a high current in a short period of time as opposed to working over a long period of time,wich you would want in a ups battery.

You would be better to buy a battery for a ups.

In theory, this is true but I am using two 175AH truck batteries discarded from our fleet of vehicles with my 24v 800W inverter and they have served me well for almost two years. These batteries are not able to supply the several hundred amps required to crank an engine but will happily supply 20amps for several hours.
The main concern would be the fact that a UPS is designed to run for a limited period of time and extended use may result in excessive temperatures in the unit. Improving the cabinet ventilation and adding a cooling fan may be necessary.

Timescope

 

^- I'm surprised to hear that. Batteries made for cranking don't do well with deep discharge/recharge cycles. Your batteries must be very heavy duty.

 

the biggest unit I added a fan to that will activate when power fails, and also on switch so should get unplugged for while fan won't kill battery. other 2 smaller ones I think existing heat sink should do. those would just be for TV, game console, DVD, and another for my workbench light, bench supply, etc. good idea though I need to ad intake holes for fan, and while at it do same on small ones.
biggest issue right now is tying to figure out how to setup in the room. stuff is kind of spread out, and I have very little 10AWG or bigger cable, so think may use extension cord since 15A i125V instead of 25+A at 12V.
I don't much care if battery fry's, as ling as don't blow up or burn or something.
we don't lose power that often to even really warrant this, but figure have the stuff cost little if anything so be cool project to try. may make an instrucable (www.instructables.com) from it if I end up going for it.

 

with these UPS this will make 6 UPS I have been given. 5 of them are APCs, and one best. looking AT APC I think everyone thinks their the best, but I see no major difference between them and the other brand. the one APC I got was about a 2000VA 30A 125 V model. of all them that one had most issues. fried batteries (not abnormal), fried resistors, etc on the controller. and a lot of the wiring was wacky (rest of APC UPS= USA made that was china made). wiring issues: 3X12AWG cord on 30 A device, 4 12 V bats in series for 48V fuses between cell pairs 100A at 32V. battery leads 10AWG 50A 600V connectors unit wiring 8 AWG. to me seems fuses were under rated for voltage, and over on amperage, and power cord would have thought should be at least 10AWG.

that definitely changed my opinion of APC, current UPS on computer is a Philips rated I think like 300 watt runs my like 400 watt PSU system though, and an old XP system. think now if wanted UPS for home use id stick to some cheaper brands. I don't see why APCs are considerably more than a Philips, tripplite, etc.

 

^- I'm surprised to hear that. Batteries made for cranking don't do well with deep discharge/recharge cycles. Your batteries must be very heavy duty.

Yes, they are DAF Super Heavy Duty 175Ah 900 Amps.

Another reason may be the lower current requirements of my 24v inverter, 33Amps at full load, which is comparable to the normal current requirements of a vehicle's electrical system when the battery is not charging.

Timescope

 

Normally, the battery doesn't supply running current, and so for the sake of economy, they aren't made for deep discharge/recharge cycles. For example, the battery I use on my boat to run acceries is a special deep cycle type. A normal car battery would be destroyed when used as such.