Use a big UPS
Having a small UPS in each server is not normally a good idea
1) Large UPS systems tend to have better power efficiency than a lot of small ones
2) Large UPS systems normally allow the batteries to be changed while still maintaining output - this does NOT apply to most small systems.
3) Batteries are much more temperature sensitive than modern computers - if you have the batteries close to the servers then the temperature of the servers will need to be much lower (with a rise in cooling cost)
4) Batteries are limited lifespan components - it is far easier to replace the batteries in one large UPS than in hundreds of small UPS systems.
One further point - make sure that the backup generator (if present) is tested frequently - and make sure that it gets up to full output in less time than it takes for the UPS batteries to drain.