Why do I have 2 HWH

Hello to this forum...I'm new here and new to plumbing in general so please be patient with me.

I purchased a new home last year and I'm trying to make sense of the plumbing arrangement. The townhouse was built less than 10 years and was sold with the basement finished as a large rec room with a storage closet and a large washroom. A previous owner installed a jacuzzi soaker tub in that washroom and I'm assuming that's why I have 2 hot water tanks in the utility room (also in the basement). Although having a jacuzzi tub appealed to me when we bought the house, we've used it exactly twice in a year.

I would prefer to not spend money I don't have to and I'm fairly sure we don't need both hot water heaters operating all the time. Our neighbors in the same complex all have only 1 tank and seem to get by with the same appliances. I imagine going down to 1 tank would be a fair savings on the electric bill. What I want to do is de-commision 1 tank. I'm quite happy the leave both tanks in place, they are beside each other and not in the way of anything else, and it would be peace of mind of have a spare if 1 packs it in at some point.

My plan is to put ball valves in the plastic lines that connect the second tank into the system so it's still connected and ready to be put into service should the need arise. It seems to me that putting a switch in the electric line and just shutting the whole thing off should be reasonably safe.

Now for the question I ultimately need to ask...what am i missing? water heater tanks are full of water all the time...if I shut 1 off and disconnect it from the water source, it's full of water that will cool off and sit there. Will this cause it to rust out prematurely? will the water go stagnant and foul, ruining the tank in a way I can't foresee? Do water heaters vent in some way I don't know posing any danger to my house and family? From the outside looking in, this seems to be safe and clever but as I stated at the outset, I'm new to all of this, its the first home I've ever purchased and I'm trying to smart about the choices I make.

Thanks in advance for any assistance.

I think if you found the hwh that served only the tub I would valve it off, cut tees and ball valves into the existing townhouse lines shut off the power and drain the tank .if the other tank let go you could just open valves fill the tank and you back online.....I would fill and flush the tank you valve off every once and a while

First thing you need to do is figure out what each existing heater is supplying. If you are lucky one of them will only feed the jacuzzi.
You need to make sure the heater you shut off supplies the tub only. if it supplies more than just the tub you will need to couple the lines from the terminated heater to the one you are going to use, or whatever was being fed by the heater you kill will no longer have hot water supply.