Our M6 was a daily driver since first purchased in about 1990. Then around 2002 it became a garage queen. We now put about 2000 miles per year on it. The problem with this is the battery is dead on this car in 2 weeks. In 3 years I've killed 3 new batteries due to forgetting charge the battery or leaving it connected and frying the battery. This running it dead leads to sulfation of the battery. This gets kind of expensive, especially since I tend to buy the oem Douglas batteries.

I bought a "Battery tender" battery charger to alleviate this problem. It's a smart charger and can be left connected and running on the battery. It brings the charge voltage down to 13.2 volts once fully charged. With the lower voltage it prevents over charging and gassing which can happen with trickle chargers. It comes with a quick connector you can install at the battery terminals. Below is the waterproof version, one of many models. I hope this saves me from performing CPR by jump starting it or having to convince the guy at the battery counter he should give me a new battery because I kill it.

The charging amperage is .80 amps so don't expect this to be your main charger. Unless you want to wait a couple of days.

I purchased the Battery Tender at Pep boys. Or try battery tender.com if you need a larger output.

Update: It has now been over 9 months and I have never had any problems with a dead battery. The Battery tender has alleviated my problem so long as I remember to hook it up.