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Basically I want to replicate the components used in car door locks using a key fob. Most of the components readily available are 12V, but small 12V batteries aren't readily available.

So I searched Amazon for wireless relay with remote and find several transmitter (fob) receiver combinations. My problem is what should I do on the receiver end to get the 12V I need to power both the receiver and the solenoid? I could 1) combine a 9V battery with two 1.5V batteries to get 12V 2) combine two 9V batteries and use a voltage regulator to drop the voltage to 12V 3) combine two 9V batteries and use a buck converter step down module to drop the voltage 4) use one 9V battery and use a step up converter to get to 12V.

I'm thinking 3) is my best option but I don't know what I'm doing. The solenoid doesn't have to be very strong and would only need a short throw ( maybe 1/4 inch).

Can anyone point me in the best direction?

The easiest way is to use this: https://www.amazon.co.uk/GP-Super-Voltage-Alkaline-Battery/dp/B072FBK3P9

If you can't get those you may find one 9V alkaline battery works okay on its own, but you may need a boost converter to get longer life.

Two by 9V alkaline battery and a 12V regulator is a cheap and cheerful option if you're not going to use it often. It might even work okay without the regulator.

There is a lot of difference between old type 9V and alkaline. The alkaline lasts much longer but has a lower voltage. The Poundland version gives the most life per cost.

In any option it would be as well to use a beefy electrolytic so there is plenty of 'shove' available when the batteries are low.

Wow. Thanks. I didn't know those existed.

I only need to pick the solenoid once or twice a day so there shouldn't be much battery drain. I think 9V would pick most small 12V solenoids or I could find a 9V solenoid. But i haven't found a 9V receiver. I asked a question about using 9V with one of the 12V receivers. They said it probably wouldn't work.

I might try the 12V batteries you referenced for proof of concept, but I would like to find a solution using commonly available batteries so I can share this with friends. Hence the questions about stepping the voltage up or down.

Then I'd go for two nine volt batteries and a 7812 regulator. mike