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Roger Heuckeroth · 04-05-2009, 09:37 AM

Firefly Batteries:

I hate to sound negative, but I have been hearing about these batteries for years. They were supposed to be available for over a year ago, but they still are not available. Also, someone on the EVDL called them and they said they were not planning on selling to the EV conversion market. I also heard they will be selling in the $400-500/ battery range.

Their spec sheet says they have an energy density of 39 Wh/Kg. Compared to Lithium that is pretty low. The LiFePO 100 Ah cells I'm using on my conversion are 97 Wh/Kg. If the $400 + price range is correct they are also not a big bargin over Lithium. Its anout half the price of a lithium pack with BMS, but they are only rated at 600 cycles at 80% DOD. Lithium can do 2000+ at 80% DOD. So they lifecycle cost of lithium is more favorable.

The biggest problem with lithium is the up front cost. Imagine if you went to the car dealer and bought a new ICE car for $20,000, however, at the time you bought it you had to pay for half the gas you would use over the next 150,000 miles. The deal would be if you prepay this gas, the actual gas you would buy at the pump would be 10% of retail price. Sounds good, but now you have to buy that $20,000 car for $30,000. This is a good deal for those that can afford it, but puts the car out of the price range of many other buyers.

When I first was looking into Lithium it was available for about $1.60/Ah. Its now down to $1.1 Ah. That's for the cells alone, not including BMS. I'm paying about $1.60/Ah for the whole pack with a really high tech BMS and charger delivered cost.

I've tested a 100 Ah cell and it can put out up to 300 Amps continuously, and can do short intervals of over 500 amps. If I stepped up to a 200 Ah cell it could do 600 amps continuous and up to 1000 amp short intervals. That's some serious power, and your not decreasing the cycle life that much by pulling that amount of current. Do that to a golf cart battery and you'll be lucky to get 200 cycles out of it.

Personally, there are only two types of batteries I would consider. Golf cart batteries, or Lithium. AGMs cost at least twice what golf cart batteries cost and don't last half as long in the typical EV application. If I was converting a small pick up truck I would go with golf cart batteries. The truck can take the wieght. For a car I would go with Lithium. Even a small lithium pack would be better than a comparable AGM pack.

Anyway, this is only my opinion based on lots of research I have done over the last two years. I'm not passing judgement on anyone who has gone down another path.

04-05-2009, 09:37 AM	#759 (permalink)
Roger Heuckeroth EV Converter Join Date: Mar 2009 Location: Saugerties, NY Posts: 51 Thanks: 0 Thanked 1 Time in 1 Post	Firefly Batteries: I hate to sound negative, but I have been hearing about these batteries for years. They were supposed to be available for over a year ago, but they still are not available. Also, someone on the EVDL called them and they said they were not planning on selling to the EV conversion market. I also heard they will be selling in the $400-500/ battery range. Their spec sheet says they have an energy density of 39 Wh/Kg. Compared to Lithium that is pretty low. The LiFePO 100 Ah cells I'm using on my conversion are 97 Wh/Kg. If the $400 + price range is correct they are also not a big bargin over Lithium. Its anout half the price of a lithium pack with BMS, but they are only rated at 600 cycles at 80% DOD. Lithium can do 2000+ at 80% DOD. So they lifecycle cost of lithium is more favorable. The biggest problem with lithium is the up front cost. Imagine if you went to the car dealer and bought a new ICE car for $20,000, however, at the time you bought it you had to pay for half the gas you would use over the next 150,000 miles. The deal would be if you prepay this gas, the actual gas you would buy at the pump would be 10% of retail price. Sounds good, but now you have to buy that $20,000 car for $30,000. This is a good deal for those that can afford it, but puts the car out of the price range of many other buyers. When I first was looking into Lithium it was available for about $1.60/Ah. Its now down to $1.1 Ah. That's for the cells alone, not including BMS. I'm paying about $1.60/Ah for the whole pack with a really high tech BMS and charger delivered cost. I've tested a 100 Ah cell and it can put out up to 300 Amps continuously, and can do short intervals of over 500 amps. If I stepped up to a 200 Ah cell it could do 600 amps continuous and up to 1000 amp short intervals. That's some serious power, and your not decreasing the cycle life that much by pulling that amount of current. Do that to a golf cart battery and you'll be lucky to get 200 cycles out of it. Personally, there are only two types of batteries I would consider. Golf cart batteries, or Lithium. AGMs cost at least twice what golf cart batteries cost and don't last half as long in the typical EV application. If I was converting a small pick up truck I would go with golf cart batteries. The truck can take the wieght. For a car I would go with Lithium. Even a small lithium pack would be better than a comparable AGM pack. Anyway, this is only my opinion based on lots of research I have done over the last two years. I'm not passing judgement on anyone who has gone down another path.