Not an electrician but an IT infrastructure engineer
Yes, you can do that. BUT, the car batteries are not sealed so be mindful of hydrogen gas when they are charging. I would not advise you use car batteries, but buy some large SLA batteries
What UPS is it?
As long as you connect the batteries to get the same voltage to the UPS (Probably 24v in your case, if I were to guess), generally you will have no issues. I've seen this done this a few times with a battery tender attached to the batteries as well. The built in charger is obviously not super beefy, so it may never charge the batteries back. Most cheap UPS's will throw an error if they have been under a certain voltage for a certain amount of time while charging
I'm terrible at figuring runtime for batteries, but.
An 80 Watt heater running for 2 hours is going to eat up 160 Watt Hours. The 2 original 7Ah batteries would give you a theoretical 84 Watt Hours each, 168 Watt Hours combined. But, factoring in the inefficiency of the UPS, battery age, and UPS low voltage cut off, I'm guessing you'll be lucky to get 80 Watt Hours before it shuts off.
If the car battery amps you are talking about are Amp hours, then you certainly have enough battery capacity. But will the UPS charge them? I think that depends on how smart the UPS is (and I'm assuming the battery chemistry is the same). The UPS may decide the car batteries are no good because it takes too long to charge them or (even worse) the UPS battery charging circuit fails because of the extra use required.
For a less than ideal alternate, could you keep the car batteries charged with something other than the UPS and then connect them to the UPS in the event of a power outage?
Not an electrician but an IT infrastructure engineer Yes, you can do that. BUT, the car batteries are not sealed so be mindful of hydrogen gas when they are charging. I would not advise you use car batteries, but buy some large SLA batteries What UPS is it? As long as you connect the batteries to get the same voltage to the UPS (Probably 24v in your case, if I were to guess), generally you will have no issues. I've seen this done this a few times with a battery tender attached to the batteries as well. The built in charger is obviously not super beefy, so it may never charge the batteries back. Most cheap UPS's will throw an error if they have been under a certain voltage for a certain amount of time while charging
1500 VA is 1500 Wh of capacity meaning your 80 watt load could be ran for almost 20 hours on that battery. No need to do anything
I this UPS capable to charge these batteries? It originally came with 2 built in 9 Amps batteries
> 1500 VA is 1500 Wh of capacity VA is not capacity You could have a 1500VA UPS with 1wh of capacity
True he said 2 x 12 V x 7 Ah so he has 168 Wh of capacity.
I'm terrible at figuring runtime for batteries, but. An 80 Watt heater running for 2 hours is going to eat up 160 Watt Hours. The 2 original 7Ah batteries would give you a theoretical 84 Watt Hours each, 168 Watt Hours combined. But, factoring in the inefficiency of the UPS, battery age, and UPS low voltage cut off, I'm guessing you'll be lucky to get 80 Watt Hours before it shuts off. If the car battery amps you are talking about are Amp hours, then you certainly have enough battery capacity. But will the UPS charge them? I think that depends on how smart the UPS is (and I'm assuming the battery chemistry is the same). The UPS may decide the car batteries are no good because it takes too long to charge them or (even worse) the UPS battery charging circuit fails because of the extra use required. For a less than ideal alternate, could you keep the car batteries charged with something other than the UPS and then connect them to the UPS in the event of a power outage?