Yeah, I have an old Shumacher 10amp charger that I used back in the day to charge up my batteries .... and it would definitely boil a battery dry if left on too long.
My current Minn-Kota 220 would likely do the same, as it's not digital, but I don't leave it running any longer than it takes to get green lights all around. Even when the boat is put up for the Winter, I just charge them back up once a month. So far that's kept my batteries in good shape for the last 3-5yrs. But if it ever craps out on me .... I'll get a digital smart charger, for sure.