The N-19 SALTWATER is a lightweight, high power and high performance DPV, but it does have trade-offs when compared to the traditional UV scooters, and additionally the Nickel Metal Hydride batteries which are at the heart of the machine have many compromises when compared to Lead Acid Batteries:

LEAD ACID	Nickel Metal Hydride
At end of dive, lead acid batteries gradually become slower, allowing the diver to safely return to the shore of boat if the burn time 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 completely shut off requiring the scooter to be towed or swum back to shore.
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 relatively new technology, hence they are more expensive. Also, they may be obsolete in less than 10 years, replaced by lithium chemistries.
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 manufacturers claim up to 100 cycles. In a deep cycle application, however, expect closer to 300 cycles.  Shelf life: don't expect more than 3 years service life out of any battery chemistry.
Lead acid batteries are double the weight of similar capacity NiMH batteries.	NiMH batteries are lighter than lead acid batteries (This allowed us to build a 60 to 120+ minute N-19)
Genesis lead acid batteries recover well from over discharge, if re-charged as soon as possible.	NiMH batteries 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. Our NiMH scooters have a low voltage protection circuit to prevent over discharge. However this in itself is another failure point which does not exist in the lead acid scooters.
Lead acid batteries are really easy to charge, and have an extremely low rate of self discharge. Only problem with charging is if ambient temperature is less than about 5 degrees Celsius.	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 noticeable amount of capacity during the first few hours after charging.
Lead Acid batteries perform and charge better the higher the temperature (up to a temperature of about 55 degrees Celsius)	Nickel Metal batteries are extremely difficult to charge to full rated capacity if the ambient temperature is high. ie, if it's hot, don't expect full capacity.
Lead acid batteries are not prone to mechanical damage	NiMH "packs" contain multiple individual cells which are connected by spot welded nickel tabs, (20 tabs, 40 welds) and each connection is a failure point. As of June 07 we have seen < 1% this kind of failure in our packs.
Our lead acid scooters do not use fuses to protect the batteries.	We do use a fuse on our NiMH packs and this is point of failure. Our UV-N-37 scooters have 2 separate packs, and the scooter will still run on the remaining pack if the other pack's fuse has blown. (as opposed to some competitors)
Unaffected by temps up to 110 degrees F	Performance degrades if stored at high temperatures.
Extreme low maintenance, re-charge every 3 to 6 months in storage	Very high maintenance. Packs need to be "exercised" every 3 months to maintain capacity.

We also want to inform divers, especially those used to the incredibly stable UV-26, that one of the trade-offs when choosing the N-19 is stability and torque offset... the N-19 is manoeuvreable, yet relatively unstable. This is true of any scooter 50 pounds or less.

With the N-19 there is no torque offset, so the smaller scooters are not recommended for those doing long dives; this is also why it's a questionable idea to make a small scooter with a huge runtime over 2 hours... the diver will be physically exhausted.

By comparison, you could scooter with a UV scooter for 3 + hours without any fatigue: you can completely let go of these scooters, and they will not veer of course for some time: they are incredibly stable, and require no diver input to maintain course, they require no more effort to guide than an automobile on a highway.

NiMH "memory" effect.

If NiMH batteries are not used regularly (bi-monthly)  there will be a temporary reduction in available capacity. Technically this may not be a true "memory" effect but a voltage depression. Ether way, the result is reduced run times. We have had a few calls from divers who have only had 30 or 40 minutes runtime. After the packs have been "exercised" 1 or 2 times, the full capacity has returned, and along with it 70 to 100 minute runtimes.

To correctly exercise the packs, we recommend the use of our burntester and watts up meter. This way you can cycle the pack once or twice until it returns to it's maximum available capacity. Burntesting should be used infrequently as it will decrease the longevity of the pack.

Expected life of NiMH batteries: 

Whilst it is theoretically possible to achieve hundreds of discharge cycles from NiMH packs (or indeed any re-chargeable battery) the expected lifetime of a NiMH (or Lithium) pack is limited to approximately 3 years. Furthermore, the capacity over the lifespan of any battery is not constant. During the first 12 months, expect at least a 20% reduction in capacity. If the battery is stored at temperatures below 20 degrees Celsius or 70 degrees F, this will prolong the average life expectancy.

Here are some approximated, no BS ranges of NiMH expected capacity over a lifetime:

0-12 months: 70 to 100% capacity

12-24 months 60 to 75% capacity

24-36 months 50 to 65% capacity

36 to 48 months : end of expected life. (Loss of 50% capacity or more).

As a comparison, we have seen Genesis lead acid batteries with HIGHER capacity after 12 months, than when new. Indeed, it is not uncommon to have Genesis lead acid batteries performing at 80% capacity after 3 years, something NiMH or common Lithium technologies can not even approach. The ONLY reason to choose NiMH or Lithium is WEIGHT. Genesis lead acid wins hands down in simplicity, longevity, robustness, reliability and affordability.