Confused On Type Of Batterys To Use

LiFePO4 is best for the purpose. Also LiPoly are OK (newer designs). You'll need dedicated charger and to adjust cutoff(low power) on the controller, because these types of batteries have different rate of discharge comparing to SLA(you can discharge them 85-95 % of their rated capacity). If you buy already built pack (with BMS) , switching is straight forward.

Ping battery packs have a good rep !

PingBattery items - Get great deals on 36V LiFePO4 Batteries, 48V 24V Battery items on eBay Stores!

LiFePO4 ALL THE WAY.

Hi VMW - I have a 24V 350W brushed motor that I powered with 2 12V 12ah SLAs. They weighed 16 lbs. In the beginning I could go 15 miles pedaling/motor but they quickly lost power so toward the end I could only go 6-8 miles. I bought 2 12V 20ah LiFePO4s. They weigh 13.2 lbs, so I got 67% more power for a few pounds less weight. They cost me $240 from Elite Power Solutions. That's without BMS (battery management system), which is a way to maximize the use and life of these batteries. I bought a smart charger for about $60 and an individual cell monitor for another $15, but you might be smart to buy the BMS that's available with the batteries.

I used 12+ ah to go almost 21 miles so I could go more if I wanted. I try to stay below 80% DOD (depth of discharge) so that's 16 ah max.

They are rated for 2C continuous, or up to 40 amps. The max my motor draws is about 28 amps or 1.4C, so they work well for me. I did some rough calculations and figure your 750W motor would probably draw 40 amps max, so you could probably get away with these batteries if you wanted to. You can go lighter and get a better C rate with other types of lithium batteries, but there ore other trade-offs. There is a battery forum on Endless-sphere.com where they discuss these issues ad nauseum if you are interested - jd

jdcburg said:

Hi VMW - I have a 24V 350W brushed motor that I powered with 2 12V 12ah SLAs. They weighed 16 lbs. In the beginning I could go 15 miles pedaling/motor but they quickly lost power so toward the end I could only go 6-8 miles. I bought 2 12V 20ah LiFePO4s. They weigh 13.2 lbs, so I got 67% more power for a few pounds less weight. They cost me $240 from Elite Power Solutions. That's without BMS (battery management system), which is a way to maximize the use and life of these batteries. I bought a smart charger for about $60 and an individual cell monitor for another $15, but you might be smart to buy the BMS that's available with the batteries.

I used 12+ ah to go almost 21 miles so I could go more if I wanted. I try to stay below 80% DOD (depth of discharge) so that's 16 ah max.

They are rated for 2C continuous, or up to 40 amps. The max my motor draws is about 28 amps or 1.4C, so they work well for me. I did some rough calculations and figure your 750W motor would probably draw 40 amps max, so you could probably get away with these batteries if you wanted to. You can go lighter and get a better C rate with other types of lithium batteries, but there ore other trade-offs. There is a battery forum on Endless-sphere.com where they discuss these issues ad nauseum if you are interested - jd

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The more I read about those batteries the more I think they should have a BMS.

A good charger too. Not a $16 eBay charger.

Nice price on those batteries !

I agree about the necessity of a good BMS and a good charger. However some say the BMSes included with some batteries are not reliable and can cause more harm than good. If a BMS fails, you are either stuck with a good battery pack that won’t work because the BMS shut it down or (worse) one or more cells overcharge or over-discharge and get ruined. So I've made my own BMS. It consists of a Celllog 8M ($15 from HobbyKing.com), a Turnigy 8150 balancer-charger ($42 at HK), a power supply for the 8150 and some connectors. The Celllog can monitor all 8 cells of my 24V pack. It has a programmable low-voltage alarm as well as an external alarm circuit to connect it to a warning light, a louder buzzer or even to a shutoff on the controller. So if a cell gets too low, I will know it. The 8150 can charge at 7 amps and has an autobalancing function that bleeds down high cells while charging the lower ones. If you don’t have a balancing charger, there is a programmable high voltage alarm on the Celllog that can be rigged to shut down the charger when any cell reaches an upper voltage limit.

These work well for me with my 8 cell 24V system. If you run 36 or more volts, then you will need multiple Celllogs and you might have to charge your pack in 2 parts. There are also some aftermarket BMSes that are reportedly more reliable - jd

thank you all. Have learned much.