Replacing UPS 9Ah with 105Ah

Other Hardware General Electronics
1

I have a small home office and after 5 or 6 years, found the UPS lasting only a 2-3 minutes when the power died this afternoon. Previously it used to run 2 PCs for about 15 minutes. Last had to use it about 2 years ago, so I am assuming that the batteries have passed their prime.

I am looking to replace the batteries, but was thinking about 'upsizing' the existing batteries to something a lot larger, as I would like to add on the CCTV DVR and some emergency lighting to the system.

The existing specs are :

Model ME-1400-BK
Capacity 1400VA / 840W
Voltage 230VAC
Modified Sinewave
Batteries : 12V9Ah x 2

Now I understand that the circuitry in the UPS is probably not designed to charge a 105Ah deep cell battery, but what if I was to externally charge to 105Ah ( say, with an automotive battery charger ) and then connect it to the UPS to keep it topped up. A monthly exercise would be to remove the UPS mains power, use the batteries, connect to the charger and re-charge, reconnect to the UPS.

Can you foresee any drawbacks with this approach ?

My thinking is that, the 1400VA system can run 2 PCs ( 200W each = 400W ) for around 19 minutes ?

My understanding is :
12V9Ah x 2 batteries = 12V x 18Ah = 216W / 400W ( 2 PCs ) = 0.54hr x 60% pf = 0.324 hr ( 19 minutes )

If the calculation is correct, with the larger battery, I could run :
2 x PC @ 200W each = 400W
Router 20W ( guesstimate )
Hub 10W ( guesstimate )
Cordless Phone 10W ( guesstimate )
Backup Lighting 15W x 5 = 75W

Total required = 515W

Therefore, usage time should be :
12V105Ah = 12V x 105Ah = 1260W / 515W = 2.54hr x 60% pf = 1.47 hr ( 88 minutes )

comments please ..

2

I have seen it done. It does work. But you ahve the correct thought of taking it out, testing-using the battery. The problems ive have seen are ,

  1. the charging system of the UPS wasnt ment for that kind load to recharge
  2. the ( even thought it will be outside of it) parts arent ment to be around the off gas of the wet cell battery
  3. the UPS Heat sink and regulaters were kinda designed around the shorter power outages (15min type)
    Those are what ive ran into.
3

My dad replaced the battery in his with two full size car batteries, and while he hasnt tested the time it lasts, it hasnt faulted in keeping it topped up the past year

4

Whatever you do, you -do not- want a wet-cell battery inside your house; all batteries when charging vent fumes and such, but wet cells can be particularly nasty about it. Not too mention potential build-up of hydrogen gas to potentially explosive concentrations. Furthermore, spills can ruin carpets, stain concrete, etc. Such batteries should not be used indoors. Use large capacity SLAs instead.