Phil, unless that lead-acid automotive-type battery is kept fully charged it will form hard sulphates on its plates, the plates will be damaged by the associated expansion, the battery will lose capacity, and in a couple of years a new battery will become pretty much useless. Permanent trickle charge, using a proper regulated supply or better, a good automatic charger, will prevent this but only if you put it on the charger every time you finish using it. If the battery started off charged but was "showing low output" after only 4 starts, it has had the gong. It should start that little engine a couple of hundred times before it has low output.
