I have been reading Electric Bicycles by David Henshaw and Richard Peace. I find it slightly worrying what it was saying about the reliability of the battery systems, in particular of Li-ion battery systems. IIRC, it said lead acid batteries were cheap, but heavy and could be damaged by running them flat, overcharging them or leaving them uncharged for months. NiCd batteries carried a bigger charge weight for weight, but could develop charge memory if they were not totally discharged each time, so that afterwards, you could not get full range out of your battery. The biggest concern though, were the Li-ion batteries. These have the highest charge density, but they're just not very reliable at the moment. They keep failing far quicker than they're supposed to. The price is starting to creep up as the demand for lithium increases. They can also catch fire in a dramatic way. All in all, it seems to be that NiMH is the best battery systen to go for at the moment. I was surprised to find the GoCycle used this type of battery when I saw them at the local bike shop. The unreliability of these battery systems is a concern, because with all the industry research in this technology, you'd have thought it would be cracked by now. We need to move over to electrically charged vehicles in order to reduce consumption of fossil fuel, and to make use of renewable energy when it's available in order to manage supply and demand.