I will not be driving my 2010 RX350 for several months. Does it matter if I disconnect the positive or the negative? What size wrench will I need?

 

I usually detach the negative terminal cable but it should not matter.

My wife's 2015 RX350 takes a 10mm wrench.

Are you going to put your battery on a battery tender? If the vehicle will be out of commission for more than two weeks, I sure would.

 

If you use a battery tender, then you should leave the battery connected to the vehicle.
You can find a battery tender for around $21 - $30 online.
https://www.harborfreight.com/12v-de...ger-62813.html

 

You're supposed to disconnect the negative first for safety reason. So if you are disconnecting only one terminal, and leaving the battery in the car, disconnect the negative.
Battery tenders are useful if you want to leave the battery connected in the car, but if you're disconnecting it from load, it's better to not use it.

 

Plus 1 on the battery tender, minimum investment, great protection, keeps the battery fresh.

 

Thanks, RX!

 

If the car is parked outside you could also consider a solar battery maintainer. You still have to connect it to your battery and run the small cable (smaller than an electric lamp cord) out of the hood and through the closed door to the solar panel that sits on the dash top. Most have a quick connect to separate the two parts. Harbor Freight or Amazon or even Home Depot online has them.
I have one as I have been car sitting for friends who go to Florida for extended periods and it works very well.