| 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 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 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. |
| low maintenance, re-charge every 3 months in storage | Very high maintenance. Packs need to be "excercised" every 3 months to maintain capacity. |
SCUBA DPV, SCUBA SCOOTER