Okay, I know this is bad, but how bad? I have 4 6v 7.2ah SLA batteries and I need 36v, maybe 48v. A buck convertor is not an option, it has to be more batteries. Locally I can buy 12v 7ah batteries for $34 each and 7.2ah for $60 each from a different retailer. So obviously I would prefer the 7ah battery/ies. I'm probably better off buying all new batteries but $ is tight right now. The 6vs are of varying ages but have been kept float charged and are in good condition. I wouldn't dare put 7.2ah in series with 4ah but how much difference can 200mah make? Any thoughts?