I have the charger velcroed to trunk carpet on passenger side. There is a small shelf in the SL63 there. I leave it plugged in when not drive by for more than 4 days. Over winter it’s all the time. I run the power cord out through the trunk rubber seal and lid when needed. I store cord in netting in trunk passenger side when not using.

As far as I know your charger should cool down as your battery reaches it’s normal charge. When left unattended your accessories battery will faint within too short a time, as the car’s systems draw current continuously. Two weeks or so seems to be the max.

I have a quick disconnect on my Ctek battery tender and if I'm not driving it the tender is on, same as my motorcycle. I route the cable up to the drivers side and slip it between the gaskets that form at a point just above the rear tire. I use a microfiber to protect the paint and let the tender hang near the rim.

Call me a nuisance, but damaging that light cable might pose a risk not be underestimated. Sure, 12 volts, what could possibly go wrong. Think downstream, often this is a non fused direct lead coming from a heavy battery, capable of delivering an ugly amount of current, peak or nominal. As a kid I used car battery power to heat two paper clips, for soldering. Red hot in no time at all. Be aware and be careful, folks.

(I ordered an original lead for the 12V plug in the trunk and I connected the plug -fused- to the battery. No scuffing between trunk floor board or seals).

If you pass it where I said there is no risk. With your setup, where do you plug the tender to? Thanks

Danaw, I use the 12V plug and I leave the lid ajar. (It had been freezing lately, wires get quite stiff).