[PSUBS-MAILIST] battery compensation

[hank pronk via Personal_Submersibles]

Thinking ahead, I need to reduce the weight of my deep diver.  I am now planning external batteries- lead acid in oil.  This reduces the amount of syntactic foam needed.  My deal on CNG  tanks fell apart.  The ebay seller would not honour the sale, can't blame him.   I may go with store bought syntactic foam if business looks good with 30 dollar per barrel oil, Yikes.  
I am not sure how to go about the oil filled battery set up.  I assume the batteries are filled as high as possible with water then topped up with oil, then the compartment filled with oil and a rubber lid on that.  I assume you take a syringe with distilled water to top the batteries up from time to time.  This way you wouldn't have to drain the oil.Does anyone know how heavy a battery weighs under water compared to in air?
I also am thinking about having the reversing relays for the motors in the oil tank to reduce the amount and size of wires penetrating the hull.  I will just send small wires for messaging to the relays.Hank
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