Does customising MacBook Pro 13inch to 16GB RAM, i7 7th gen processor and 1TB SSD affect it's battery life?
The only upgrade that may impact on your battery life is the processor upgrade. However, while some i7 CPUs are quad-core, the ones offered on the 13" MBP are dual-core processors, just like the i5 CPUs.

Since all dual core i5 and i7 mobile processors support hyper-threading, there's actually very little difference between them in terms of a performance gap and battery usage. In fact, both options for this model also incorporate the same Intel Iris Plus Graphics GPU. 

My personal recommendation would be to go with the upgrade if you can afford it, as it will increase it's longevity in terms of future compatibility with software/hardware.

If you had to pick and choose what you upgraded, then the upgrade to 16GB RAM would be the most useful.

Finally, you may want to know that Apple's battery testing for this model was conducted on the following configuration:


2.3GHz dual-core Intel Core i5
1TB SSD
8GB RAM


Source: Apple