It's not necessarily due to the charger - it's hard to narrow it down to one particular variable. It COULD be that with the way you've been using the batteries and charging that 5-day's time is enough to recharge them (it probably is).Are the batteries that have enjoyed these two+ years of mismanagement under my pitiful charger now, toast?
Find out how old they are and then charge fully and load test them. Otherwise it's just a guess.