1998 Volvo V70 Battery Acid leakage in to Engine bay

Engine problem
1998 Volvo V70 Front Wheel Drive Automatic 60,000 miles

I have 2 Volvos with the same problem. A V70 1998 Non Turbo with 60,000 miles and 850 SE Sedan non turbo with 90,000 miles. Both vehicles have had new batteries fitted over the last 12 months and both have had leaking battery acid evident into the battery tray and down into the subframe. Evidence of splashing is also showing in the Engine bay. The problem is not conspicuous unless the battery is removed or an inspection is carried out underneath the front end. I only noticed a small pool of "water" one day under the car and was curious of its origin as it was not under the air conditioning outlet where dripping water is often evident. The Cruise control on one car stopped working as well. Upon removing the battery and tray in one vehicle I found significant leakage. Upon looking at the second vehicle I found the same problem. Both batteries were fitted new and are of the refillable type. I added distilled water up to the designated fill levels in both batteries over the last 12 months on one occasion which I regard as a normal operation so I assume that this may have created the problem. However upon removing the batteries in both cars and testing for obvious signs of leakage by tilting etc no liquid leaked out. My driveway is on a reasonable slope but I have owned other vehicles previously and never had this problem. I dont know how the battery acid leaks out as all the plastic fill caps are screwed in tight. There is a small drain venturi on the top of the battery which could be allowing leakage but the water level is well below this. Could the cause of leakage be related to engine use building up heat and casusing the pressure to build up inside the battery? I have never had this problem on any other vehicle fitted with the same battery type. There is also a control unit fitted to the underside of the battery tray that I think controls the Cruise control and this was badly damaged and I think is the cause of the cruise control malfunction.

Any comments would be appreciated. I will never buy a refillable battery again.

Thanks JN