Interstate (Johnson Controls) makes batteries for Sears, Pep Boys, Autozone, Sams, Walmart, Costco, etc. IMO they are good batteries and superior to the OEM Porsche battery.

 

Many chargers are not sensitive enough to tell if the battery is fully charged. If they continue to add charging current to the battery, it will boil the acid and ruin the battery, not to mention the damage by the spilled acid. Ask me how I know. . . !

Porsche's cigarette lighter charger does not do this, as the circuitry is sensitive enough to "float charge" for long periods. BMW makes a similar item and it costs about $60.00 at BMW dealers.

The nice thing about both of these is that there is no need to add clips, etc. Just use the cigarette plug.

My $0.02.