I only used to use the 172 in fair weather/weekends only and it soon ended up with a flat battery that I had to keep jump starting off the van.
Worst of all was when I went to Silverstone, i filled up with fuel about half an hour away from home and it wouldnt start on the forecourt of a very very busy Shell garage. Had to get jump started by the guy behind me in his brand new SAAB.
Embarassing.
Whilst at Silverstone, I picked up an Optimate III SP charger from the Ducati Corse shop on the circuit. Had been looking at them a few weeks prior to this and the price was good too.
These are great as they have screw on terminals that you can keep attached to the battery and there is a small waterproof rubber housing that you clip the mains cable from the Optimate into.
makes it very easy to disconnect when you want to go out and re-connect when you are back.
Very good bit of kit, had it on my car over a year and I never had any more trouble with the "dead" battery.
It fully re-conditioned it.
You dont have to disconnect the battery at all and its safe to keep on all week if you like - it wont overcharge - it monitors the voltage every hour or so once it is at its peak and only trickles if necessary.
You have to be careful with some of the cheaper ones that arent designed to be connected to the car while the battery is still connected.
Problem of getting backfeed through the rectifier, so I'm told.
http://www.accumate.co.uk/cg010001.htm