Get the device and charge that battery. The charging action is better than driving the car around to charge a discharged lead acid battery because the lead sulfate (which is brittle) will break off the plates and fall to the bottom where it can't be reclaimed back using normal methods.

BTW, starting your car weekly without driving around to warm up the engine oil to 100ºC is bad for the engine because it builds up moisture and combines with the sulfate formed during combustion (from impurities in the petrol) to form sulfuric acid. I'd rather let the car sit there for a month.