Part 3 - What kind of batteries should I use ?

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At the moment there are really only a few choices for EV batteries.

The first is flooded lead acid batteries, such as golf cart and trolling motor type batteries. While these are reasonably priced, they do require periodic water level checks and cleaning. Dollar for dollar they are the least expensive way to power an EV. For high performance EVs however, they are a poor choice, because of the weight, and inability to handle high current loads (over 600 amps) without losing service life.

The second choice is VRLA, (Valve Regulated Lead Acid) AGM (Absorbed Glass Mat). These are often used in computer backup (UPS) power systems. They are considered sealed, so there is no fluid level to check, and they stay clean, because they don't vent under normal charging. They are able to deliver astonishingly high currents without failing. They do tend to be a bit more expensive, and require more sophisticated charging systems than the flooded batteries. They also usually have a shorter service life.

The third choice is gel cell batteries. These are lead-acid batteries with the electrolyte in a gell format. Due to the methods used in manufacturing them they tend to be very consistent battery to battery within production lot. This reduces the need for the battery management systems used on AGM batteries, though many folks still recommend them on gells as well.

The fourth choice is Nickel Cadmium (Ni-Cd). These were first recharable batteries, and had the "memory" problem of needing periodic complete discharge. The toxicity of cadmium became an environmental issue. European Union banned Nickel Cadmium (Ni-Cd) batteries for several years. This is assumed to be un-viable technology. Electro Energy may have a product offering but there's no current data. SR Batteries sells high performance NiCd batteries. Cells are 1.2V up to 5Ah. Guarantee no memory effects with their batteries. Although excellent cells, the price is extremely high for a pack large enough to power an electric vehicle.

Lithium ion batteries are at the early stage of penetrating to EV market. Their long term life span is still a bit of an unknown, though it is quite promising... Lithium Iron Phosphate (LiFeO4) is much safer than Lithium Cobalt, best found on current market which is suitable for EV for more than 100 mile ranges. It requires sophisticated BMS to monitor each cell. A123 produces lithium ion batteries with high energy density, but the scale is not very big and the price is very high which makes most American not affordable for EV using A123 lithium-ion batteries, the scale-up and lower cost lithium ion batteries from Elite Power Solutions make it possible for EV to be in affordable price range and 100+ miles range.

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Next: Part 4 - What are DC controllers ?