E-150 5.8L wont start after hard rains

[Biggggbarney]

Hello, newbie here, my son has a 5.8L Ford lift van '95, when it is driven in rain it spits and sputters, I've had it almost to the floor going like 40mph. Sunday we had some of the hardest rains ever here, tried to get him to work Monday, it turned but never started. After many many attempts my turns went to a nice loud click sound when ya turn the key, I'm guessing click due to battery probably low ....... anyone have ideas on the not running after severe rain storms??? Thank you, Bryan