Most People are Looking at the Lead Acid Batteries tag or Label values - or - the 20 Hour ‘Rating’ and seeing the value (Like the 150 Ah worth of energy) and forget that means 150 / 20 = 7.5 Amps load. They really need to get the spec ‘Chart’ that shows the 20 hour, 15 hour, 12 hour, 10 hour, 9 hour, 8 hour, … > 1 hour, and if possible the 45 minute, 30 minute, 15 minute, 10 minute, and 5 minute ratings!
In my whitepapers on Electricfly - MyElectricfly.com - I just use the 1 hour ratings for comparison, but most lead acid battery makers don’t give a lot of information in a full chart - like the Surrette’s do (All sizes | Surrette-Battery-Specs_Combined-Table | Flickr - Photo Sharing! ), so most of us go off guessing what we have available, and it makes us think lead acid is so much cheaper than Lithium iron Phosphate - but - in the EV Application and loads, it’s not.
Since the plan in building an EV Conversion - should be - in my mind: Determine how you want to drive it, compare the Torque Ratings of the original Engine, with what torque is available - at what volts x amps, from the desired electric motor, and if it can deliver the torque desired - then look at the power needs Volts x Amps = Watts (divided by 1000 = kilowatts [kW]), and get a controller than can exceed that power need by 50% at least, and build a battery pack that can exceed that by at least 50% in a continuous rating. That in itself pretty much excludes all Lead Acid Batteries - and might even eliminate some of the lower cost Lithium Iron Phosphate cells in a smaller pack!
The Number of interest - is the ‘C’ Rating - continuous - for the cells, and - don’t forget - that ‘C’ Rating means two things: [1] how many times the rated energy can it deliver power: 3C = 3 X the Ah label rating, while 10C means 10X the Ah label rating and 30C = 30X the Labels Rating, and [2] - also remember: 3C = 60 minutes of run time (1C) divided by 3 = 20 minutes; and 10C = 60 minutes /10 = 6 minutes; and 30C = 60 / 30 = 2 minutes!
So - if you want range - you need to determine how much power you can deliver at something between 2C (30 minutes) and 0.5C (120 Minutes). After that - you need to work back, deciding how empty you want to drain your pack from full - or the Depth of Discharge: DOD! Most Lead Acid Batteries should not really be drained below 50%, and Lithium Iron Phosphate below 80% if you want a decent life from them: [lead Acid might give 500 - 800 Cycles, or if you have excellent batteries - maybe 1,000 cycles; while Lithium can deliver 1,000 cycles for 100% DOD, and usually about 2,000 Cycles for 80% DOD, but - at 70% DOD - even deliver some 3,000+ cycles!]
My goals are to work with a 70% DOD for normal conditions - leaving the last 10% going down to 80% DOD as a reserve. Then - since you have calculated your needs - divide by the 70% figure to get the net energy at your required loads your pack needs to store and make available.
Example - you need 300 Wh / Mile, and need to drive 50 miles - that means yo need 50 x 300 = 15,000 Watt Hours [Wh] usable. To find out how big your pack energy needs to be - divide by 0.7 [70% DOD] = 21428.57 Wh (21.43 kWh, approximately).
If your Lead Acid Batteries 1 hour rate can deliver this - you are in luck (I suspect not), otherwise select a lithium Iron Phosphate Cell rated to take the power loads describe above, and build a pack with them to deliver the total energy for your target range.
This is not cheap - but it is purpose driven - rather than experiment driven. Maybe I am wrong - but - in today’s terms - I feel that lead Acid is genuinely not cheaper than LiFePO4. >>> Electricfly - MyElectricfly.com contain my thoughts and calculations. See if you agree, or not!