Hi,
I have an Optimate charger / conditioner and have used it on my Xantia Hdi, 307 hatchback and 307cc for many years without disconnecting the battery. The instructions say it's safe to do so. I have no knowledge of battery monitoring devices and doubt any of my cars are new enough to have one. My cars only get used for occasional short runs so the battery doesn't get a chance to recharge sufficiently. Battery on Xantia is easy to get to and remove but 307 & 307cc are a pain.
A while ago the battery on my 307cc went flat and I couldn't get into the car to release the bonnet, could open the drivers door with the key but too close to fence to get in. There's an additional problem with the 307cc, when you touch the handle the window drops about 5mm to allow the door to open. I'm told you can pull it hard to force the window past the groove but knowing my luck the window would break and where to get a replacement? My Optimate charger was originally designed for motorcycles with sealed batteries which are very difficult to get to. To overcome this it's supplied with a charging lead which is permanently connected to the battery and run to an accessible point to connect the charger, this has a waterproof connector with a rubber cap. I connected this to the battery terminals and ran it through to the scuttle, where the wipers are, so I can connect the charger without even opening the bonnet. If you have a battery monitoring system fitted just connect the -ve to a suitable earth, it'll work just as well.
Regarding the use of jump leads, it's not a good idea to jump start or jump start from a modern car with electronics, if you must, do it without the engine running. If you have the engine running you need to leave the leads connected for at least 30 min, if you don't it could create a spike when you disconnect the leads which could zap the electronics in either or both cars. This happened to a work colleague with a Rover and cost him over £1000 in repairs. You may be lucky and get away with it but is it worth the risk?
There are jump leads with surge protection available but these are expensive, especially if they're only for occasional emergency use.