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Archives  from 2008:
How we compare: Product comparison N-19 and Dive-Xtras Sierra      

 

Battery Information

Lead Acid,UV-18 & UV-26Nickel Metal Hydride (N-19, UV-N-37)Lithium Polymer (Magnus)
At end of dive, lead acid batteries gradually become slower, allowing the diver to safely return to the shore of boat if the burntime has been slightly exceeded.NiMH batteries will cut-off suddenly at as soon as they have been fully discharged, possibly leaving the diver stranded. At best, the diver will always have to make the dive shorter than necessary, to ensure the scooter does not completley shut off requiring the scooter to be towed or swum back to shore.Can have a hard cut-off, or if used with a Electronic Speed Control (ESC) can have a soft power down mode, making it perform similar to lead acid. (Magnus has soft power down)
Lead acid batteries are a very mature technology, having proven characteristics of reliability and low cost. This chemistry should long outlast NiMH batteries.NiMH batteries are a relativley new technology, hence they are more expensive. Also, they may be obselete in less than 10 years, replaced by lithium chemistries.Most expensive, with the shortest track record, but with promising specifications.
The high quality Genesis batteries have 200 to 500 cycles (standard quality lead acid may not perform well after 50 to 100 cycles in a deep discharge device, such as a scooter)NiMH batteries specify 500 or more cycles. however, this is unproven in underwater scooters. Realistically, don't expect more than 3 years service life out of any battery chemistry.At least as good as lead acid; better than NiMH.
Lead acid batteries are double the weight of similar capacity NiMH batteries.NiMH batteries are lighter than lead acid batteriesLithium Polymer batteries are the lightest batteries currently available.
Geneis lead acid batteries recover well from over discharge, if re-charged as soon as possible.NiMH battereis can suffer from "cell reversal" when charged as a pack, if the individual cell voltage is allowed to drop lower than 1 volt per cell. This is quite possible as NiMH batteries have a high rate of self-discharge, meaning they will comtinue to discharge even after the low voltage protection ciruit has prevented active discharge.Electronics protect cells.
Lead acid batteries are really easy to charge, and have an exremely low rate of self discharge. Only problem with charging is if ambient tempertature is less than about 5 degrees Celcius.NiMH have as much as 10% self discharge on the first day after charge. The higher the temperature, the higher the self discharge. Unfortunately, the batteries heat up during charging, especially at the end of charge, so you loose a noticable amount of capacity during the first few hours after charging.Almost zero self discharge. Do not loose capacity from lack of use. No need to cycle to maintain performance.
Lead Acid batteries perform and charge better the higher the temperature (up to a temperature of about 55 degrees Celcius)Nickel Metal batteries are extremely difficult to charge to full rated capacity if the ambient tempertature is high.Avoid high temperatures. Easy to charge.
Legal for passenger aircraftLegal for passenger aircraft.NOT legal for passenger aircraft.








Submerge Scooters.    Jupiter, Florida USA.      Phone 561 747 3640       submerge@silent-submersion.com