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Discussion Starter · #1 ·
I've got an electric Firefly that needs new batteries. It's currently got ten Powertech AGMs, 8A24 12V 79Ah. These have lasted about 4.5 years, 250 cycles and 2500Ah total in their lifetime with occasional driving. I want to start commuting with this car, but the batteries are now too tired to get me to work. I was getting about 35Ah when new, now I'm getting about 12-15Ah.

My commute is 12km and about 15 Ah each way, and I'd be charging at work, so I'd be putting about 500 cycles per year on the pack. I'm struggling with justifying buying a new pack if it will only last a year or (maybe) two with my usage.

So far I've considered Optima blue tops, the same 8A24 Powertechs I have now, and Geltech 8G24s. All are approximately the same price at about $190-215. The Geltechs look to have the best cycle life (650 @ 50%DOD), but I'm not sure they can handle the 350A max current draw. I'd prefer to stay away from floodies because the rear battery box is hard to access for watering.

Does anyone have suggestions for what batteries I should get? The only option that seems worthwhile for my usage is lithium, assuming they actually meet their 2000-3000 cycle rating.

Thanks!

David
 

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120 volt pack nominal of lead acid. 79Ah at 20 hour rate, but you weren't quite pulling 35Ah when new. You used them 250 cycles.

In my humble opinion: Lithium batteries are your friend.
We all need some additional info to help you out though so that way we can recommend the affordable lithium to meet your needs.

120v*35Ah=4200 watt-hours Are you going about 15 miles? Is your 35Ah measurment how much you are pulling out of the pack(essentially figuring peukert), or how much you put back into the pack when charging?

What range do you want your new pack to be?
How much current does your current controller draw? ...or rather, if you are planning to upgrade your controller, how much will that one be pulling at maximum accleration?

How much amperage do you pull from your battery while cruising? Also what speeds do you cruise at?

The issue with going to lithium is that you want to keep your average C rate draw of the pack fairly low, usually a cruising amperage of about 1C unless your commute is shorter, in which case you won't draw on the pack too long to get things warmer than they should be for maximum battery life. It all depends on the commute you are running for what sort of lithium we would recommend. If you are looking to upgrade your components too, or range, or performance, it would be good to know what you are looking to do.
 

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120 volt pack nominal of lead acid. 79Ah at 20 hour rate, but you weren't quite pulling 35Ah when new. You used them 250 cycles.

In my humble opinion: Lithium batteries are your friend.
We all need some additional info to help you out though so that way we can recommend the affordable lithium to meet your needs.

120v*35Ah=4200 watt-hours Are you going about 15 miles? Is your 35Ah measurment how much you are pulling out of the pack(essentially figuring peukert), or how much you put back into the pack when charging?

What range do you want your new pack to be?
How much current does your current controller draw? ...or rather, if you are planning to upgrade your controller, how much will that one be pulling at maximum accleration?

How much amperage do you pull from your battery while cruising? Also what speeds do you cruise at?

The issue with going to lithium is that you want to keep your average C rate draw of the pack fairly low, usually a cruising amperage of about 1C unless your commute is shorter, in which case you won't draw on the pack too long to get things warmer than they should be for maximum battery life. It all depends on the commute you are running for what sort of lithium we would recommend. If you are looking to upgrade your components too, or range, or performance, it would be good to know what you are looking to do.
What is the shelf life for the LIFE's? I have been using them in lectric bikes thinking I would get the 1000 charges they are marketed as giving, but I would have to get all 1000 charges in less then 3 years, because they just go bad, regardless of how much I do or don't use them.

I drive my EV around 2000 miles a year, and at that rate I can pretty much use up LA's before the just plain get old, but I am reluctant to use LIFE's if all I get is 6,000 miles out of them before the chemistry just goes bad from age.
 

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Discussion Starter · #4 ·
Thanks for the quick replies!

120v*35Ah=4200 watt-hours Are you going about 15 miles? Is your 35Ah measurment how much you are pulling out of the pack(essentially figuring peukert), or how much you put back into the pack when charging?
35Ah was about the maximum I could remove from the pack before the voltage would start sagging excessively under acceleration. That capacity got me about 24-30km depending on driving. I only drained it that far once or twice. Based on the BMS, my average trip used 10Ah.

What range do you want your new pack to be?
How much current does your current controller draw? ...or rather, if you are planning to upgrade your controller, how much will that one be pulling at maximum accleration?

How much amperage do you pull from your battery while cruising? Also what speeds do you cruise at?
I suppose I'd be OK with about 30km range, which is about 5kWh for this vehicle. I would like more, depending on price. The present controller draws about 350A max, and cruise current is about 100-120A highway (100km/h), maybe 50A city at 50-60km/h. There is one large hill on the commute, pulling 250A for about 1 minute. Ideally I would like to upgrade to higher voltage, perhaps 144 or 168V, with a 400-600A battery current. With the present setup of 120V with a 400A 1221R controller, the performance is adequate, but I would like more.


The issue with going to lithium is that you want to keep your average C rate draw of the pack fairly low, usually a cruising amperage of about 1C unless your commute is shorter, in which case you won't draw on the pack too long to get things warmer than they should be for maximum battery life. It all depends on the commute you are running for what sort of lithium we would recommend. If you are looking to upgrade your components too, or range, or performance, it would be good to know what you are looking to do.
So based on this, I'd need something around 100Ah cells, which is what I was thinking when looking at lithium.

Like gojo, I too was also concerned with the shelf life of lithium, in addition to the cycle life. Are there any examples out there that show how long they actually last?

Thanks
David
 
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