After you clean them, put mineral oil in you batteries and you will not get any corrosion in the future. 12 volt batteries get 2 oz. 6 volt batteries get 4 oz. each cell.
It is sold as a laxative in the pharmacy dept at Walmart.
I don't know exactly why there is no corrosion except that the oil layer on top of the acid must stop the fine corrosive gases from venting through the caps.
I know, everybody says the only thing you add to batteries is distilled water, but mineral oil works to stop the corrosion and does not hurt the battery. Search this site, there has been a lot of threads on this. I have used mineral oil in my 4 golf cart batteries for 3 years, so far, no problems and no corrosion.
06 Hurricane 34FT WH W20 Chassis 8.1L 129K, Steersafe, Koni Shocks, DIY Trac Bar, Tri-Metric 2025RV Battery Monitor, 4-6V Batteries, Scan Gauge 2, Crossfires, 735W Solar Morningstar MPPT-60, KVH R5 In-Motion Sat, XM Radio, 07 Chevy Malibu Maxx Toad, Falcon 2, Brake Buddy, Escapee