Best EV Battery Configuration

by Scott Emerson
(Virginia)

I am considering what type of battery (6 Volt vs. 8 Volt) to use and what configuration to use them in (strictly series or two series packs paralleled together) and was wondering what your suggestions might be. My goal is to get the most capacity with a voltage of 96 - 144 VDC

Example 1
20 - 24 six volt batteries connected in series to achieve 120 - 144 VDC. Using the Trojan T-125. Its rated capacity at the 20 hr AH rate is 240.


Example 2
15 - 18 eight volt batteries connected in series to achieve 120 - 144 VDC. Using the Trojan T-875 its rated capacity at the 20 hr AH rate is 170.

Example 3
two packs of 12 eight volt Trojan T-875. Each pack would contain 12 batteries connected in series and then the two packs would be connected in parallel together for a total voltage of 96 Volts. Now each battery capacity at the 20 hr AH rate is 170.

My question really is in the above example 3, what would the capacity be? Would it double to become 240 at the 20 Hr AH rate? I know that the 20 Hr AH rate is not the correct rating to use when determining what type of battery to use, but I am unsure of what else to use in comparison.

Hi, Scott!
Good question.
In configuration 1, you've optimized for cycle life. With the 6 volt batteries, you'll get the most miles before you have to replace the battery pack, but it will be heavier than the 8 volt pack.

Depending on your conversion, you might be concerned about the weight of your batteries more than the cycle life, so you might prefer configuration 2.
Eight volt batteries go into your system to conserve weight. You'll get better performance and handling out of configuration 2, but you'll have to replace the batteries sooner.

Configuration 3, you've wired two series-wired packs in parallel with each other to double the amp hours, and yes, that works.

The question is, what do you need most in your car - is weight more a consideration, or do you want the most miles for your money?
Regards,
Lynne

P.S. Check out the articles up there on the right (the recommended reading) for more details on this stuff.