Analog Timer with 400 MH Ballast Overloads Surge Protector Approaching Lights Off

I just bought a new Battery Backup/UPS for my 400 Watt MH ballast (HarvestPro Switchable), as brief power flickers would cause it to turn off with a 4+ minute delay before starting up (my HPS ballasts don't seem to have this issue). As I was crawling into bed, the beeping began...

Observations
-the UPS (un-interruptible power supply) manual says that continuous beeping indicates "working under overload condition"
-the ballast and lamp were on, apparently uninterrupted
-main circuit breaker not tripped/broken, Battery Backup circuit breaker not tripped
-fan still working, turning it off didn't change anything
-the analog timer (a 2 outlet exactly like my HydroFarm model, but no logo) was on the last "on" notch, about to turn off
-the ballast turned off, the UPS stopped beeping

Possible Reasons
-the 850VA/425 Watt/1560 Joules UPS is just too small
-the cheap/knock-off timer may cause an arc or something that causes power output to temporarily increase while in the last "on" notch's position

Does anyone have any experience with similar equipment behaving this way?

The UPS is too small.

A ballast typically operates at 5-10% over whats listed. The cheap ones operate at 5-10% under whats listed. My guess is your 425 watt UPS is probably truly overloaded. If you have a dimable ballast, try turning it down a notch or two, this should solve that. If its not a dimable then your kinda SOL on that.

Definitely put the fan on a different plug though. I would unplug the fan, and cycle the UPS and ballast to see if it makes a difference, if not, get a bigger UPS... Or to solve your power flickers, replace your breaker in the breaker box... Should be alot easier than buying a UPS.

- Edit addition:
Wanted to add, that just like ballasts, cheap UPS's can operate over or under specifications. You might only be getting 385 watts out of it. Another option... Open the UPS and remove the stupid little speaker.

Thanks for the reply low_ryder.

I think you're right that I need a bigger UPS, as it can't handle anything more than a flicker (thought I had a larger one on the way, but 9 days later MicroCenter says it's unavailable, lol). This one can go in the nursery. There may be a power spike just before the timer cuts off, but ultimately the power allowance is still too close for comfort (and a larger UPS is needed).

Also, I think changing the 15 amp breaker out for a 30 is inevitable, but I hadn't realized that could be the cause of the flickers.

I swapped my 20 out for a 50 on my 936w grow. It only tripped when the TV in that room was on, but that was still often enough.