The original back-up batteries for TS1s did not last long.
I use rechargeables in my TS1 (800mah). Batteries last long enough in an outage, approx. 4-6 hours or so (the backlight is what kills the batteries fast, so 30sec to 1 min is what you want to set it as), then I simply pop in fresh rechargeables, and put the old ones on the charger (I rotate through 3 packs…12 batteries).
That said, I wouldn’t buy a newer TS1 since it lacks battery backup. You can get the older ones (says “Emergency” under button) new off places like eBay. As far as I can tell, there is zilch difference between the two hardware versions other than the cosmetic button names/symbols, and battery/no battery with barrel plug. UPS to me is not a better option. That’s just me though. I would use a PAD1 before a UPS.
But for those without that option a good UPS runs around $1,000, but you can get a cheap one at staples for $40 (9 min run time, maybe hour if just the TS1). $100-$200 UPS may double that time.