So I ended up needing to get one of these because I'm off work and stuck at home having broken my ankle in 2 places quite badly meaning I can't drive. Recovery time is about 3 months so I needed to make sure my BMW 5 Series stayed in a workable condition.
I've never had a battery charger or any trickle charger/maintainer before but someone mentioned I should get one so I went looking into it.
I checked a lot of different products including BMW own brand (and almost bought that for piece of mind) but then stumbled across this at almost 20% cheaper than most products of a similar nature, and it had decent reviews too, so I bought it.
On arrival, unpacking showed I have 2 connection options - croc clips for easy-to-remove connection to the +/- terminal points in the bonnet or actual clamps that screw on for a more "permanent" option. I went for the crocodile clips. The unit itself is tiny and IP65 rated to be used outside in fully waterproof and dustproof casing.
The lead was about 2m which was JUST enough to reach from my driveway into my kitchen window but I need to use an extension lead up to the window to get it to a power socket - the cable could have been a lot longer.
Connected up and following instructions - which were very easy to follow - I switched it on - it has a very simple panel - a circle button to switch power modes (it automatically selects 12V and my car needs 12V so did not touch this button at all), and a start play button.
If at this point you've not connected the Battery Maintainer up correctly it apparently will beep loudly to let you know and one of the lights on the unit lights up RED.
It spends the first few hours after hitting play button it assesses the condition of the battery before moving to a trickle charge mode. It took almost 2 days but it slowly charged my battery back to 100% and in the morning on the second day I heard a beep outside - that was the unit telling me it's charged.
At this point the unit changes itself to a FLOAT mode. This keeps the battery at 100% condition very carefully using minimal power to do so - I've left the unit for a week now on this setting. This will help desuplhur the battery too as when left to run low, sulphur can build up and damage the efficiency of the battery.
This is a great piece of kit all round. It is keeping my battery maintained in perfect condition while I'm unable to drive it for 3mths giving me piece of mind and a worthy investment as it's something I should have bought years ago!
The only negative is the lead being only around 2m (1m each side of the unit) - it should be at least twice that length in my opinion, though if you have a garage with a plug point inside it wouldn't be an issue.