Powering 12v solenoid with 4 18650’s?

I am building a automated cat feeder with a Arduino. I’m done with the programming and most of the electronics is figured out. For the water I have a relay close at a certain time to give power to a 12v solenoid that pulls about 1 amp.

For power I have 4 18650s in series and I’m going to wire that to a buck converter for a constant 12v

My question is having the batteries in series to the buck converter to the solenoid, will there be any problems with that set up?

For a relay, you don't need the voltage converter. The 12V is nominal, and it will operate safely over a fairly wide range of voltages, so you may find that 3x18650 in series will work fine.

However, you do need a battery protection circuit that prevents the batteries from being discharged below about 3.0V each, or they will be destroyed.

Finally, the relay is a waste of power. A logic level MOSFET is much more efficient for switching such a simple circuit. A typical configuration is shown below.

Ok, I was thinking about doing away with the converter. I just have the relay to interrupt the power to the solenoid until the Adruino tells it to close at a certain time for feeding. Thanks I will look into a battery protection circuit. That’s really cool. I will try that instead of a relay. Thank you

Series circuits with lithium based batteries are for experts. They need proper charging and charge balancing as well as protection circuitry and are dangerous if mistreated.

It is much better and safer to use 6 to 8xAA alkaline batteries and plan on replacing them from time to time.

Thank you for the suggestions.That makes sense. That’s why I put a post on here. I bought a 4x 18650 battery holder without much thought on what needed to be done for safe operation. I’m trying to avoid throw away batteries.
What about a small 12 v lead acid battery that I can recharge with a 12v charger. Like this

12V lead acid batteries, especially gel cells, are a good choice. They are very tolerant of abuse. NiMH are also good and can be trickle charged for very long periods of time.

Lithium batteries do not tolerate mistreatment, and can be quite dangerous (as you probably know).