Jeremy Harris
100 MW
OK, I absolutely do not want to see this thread denigrate into another slanging match about sales techniques etc!
I've been trying to establish what the really important, simply expressed, attributes of an ebike battery are and see how we can best make trade-offs to match our personal circumstances. I've ignored reliability, because there doesn't seem to be enough data around to make a judgement. The idea was to look at selecting a battery based on personal requirements, making sure that all the really important things were picked up.
Capacity
Very important, as useful capacity, at the average operating current, is the only thing that matters. Theoretical capacity is meaningless, it's only the Ah you can actually get out of the battery that is any use. SLAs seem the worst, some Lithium technologies seem to be the best.
Max continuous discharge current
Pretty important, as this often has a major bearing on useful capacity. Discharging a cell at more than it's rated current will result in less useful capacity.
Weight
Important, probably more so than volume for any given capacity, as bike handling and performance is directly related to weight.
Cycle life
Important up to a point, but a comparison needs to be made between cycle life, probable use and calendar life to work out how significant it is in each individual case. Cycle life is only meaningful if it represents full charge/discharge cycles. For many battery technologies, like NiMH, limiting charge/discharge cycle depth can easily extend life into the hundreds of thousands of cycles (see the Toyota Prius case, for instance). If we want the maximum useful capacity from a battery then it's vital that we understand the effect this has on life.
Calendar life
Often overlooked, but most probably more important than cycle life for many (most?) ebike users. For example, a battery than has a 1000 cycle rated capacity life, but a two year rated capacity calendar life, will most probably die of old age before it dies from being over-cycled. I doubt that many users will average more than 300 cycles a year on a battery (although accept that a few might). If your riding pattern means that you're only going to average 100 battery cycles a year, then calendar life almost certainly completely dominates when it comes to battery selection.
Volume and shape
Probably the least important attribute in practical terms, as even worst case batteries in this regard seem to be able to find a home on some bikes. Shape may be more important than volume, as cells that can be re-arranged to fit the frame space available will be simpler to use than those batteries that come in big, fixed size, blocks, like SLA.
Cost
Importance depends entirely on the means of the purchaser. Some will pay a premium to get exactly the battery they need, others may choose to trade some of the above to get what's affordable to them.
For me, useful capacity, weight and calendar life are the three key attributes, as I doubt I'll ever achieve more than 100 cycles a year on average. My riding is a short daily commute, with an occasional longer ride. I can go three or four days on 10Ah without recharging. Weight was pretty important, as my 'bent handles badly when weighed down. For my initial experiments I didn't want to spend heaps of money, in case things didn't work out, so I opted for cheap batteries. If these work OK then I will look to upgrade to some with a better calendar life as soon as the cheapos start to fade.
I guess we'll all have differing views on the "best" battery, as all of us likely to want different things from one.
Jeremy
I've been trying to establish what the really important, simply expressed, attributes of an ebike battery are and see how we can best make trade-offs to match our personal circumstances. I've ignored reliability, because there doesn't seem to be enough data around to make a judgement. The idea was to look at selecting a battery based on personal requirements, making sure that all the really important things were picked up.
Capacity
Very important, as useful capacity, at the average operating current, is the only thing that matters. Theoretical capacity is meaningless, it's only the Ah you can actually get out of the battery that is any use. SLAs seem the worst, some Lithium technologies seem to be the best.
Max continuous discharge current
Pretty important, as this often has a major bearing on useful capacity. Discharging a cell at more than it's rated current will result in less useful capacity.
Weight
Important, probably more so than volume for any given capacity, as bike handling and performance is directly related to weight.
Cycle life
Important up to a point, but a comparison needs to be made between cycle life, probable use and calendar life to work out how significant it is in each individual case. Cycle life is only meaningful if it represents full charge/discharge cycles. For many battery technologies, like NiMH, limiting charge/discharge cycle depth can easily extend life into the hundreds of thousands of cycles (see the Toyota Prius case, for instance). If we want the maximum useful capacity from a battery then it's vital that we understand the effect this has on life.
Calendar life
Often overlooked, but most probably more important than cycle life for many (most?) ebike users. For example, a battery than has a 1000 cycle rated capacity life, but a two year rated capacity calendar life, will most probably die of old age before it dies from being over-cycled. I doubt that many users will average more than 300 cycles a year on a battery (although accept that a few might). If your riding pattern means that you're only going to average 100 battery cycles a year, then calendar life almost certainly completely dominates when it comes to battery selection.
Volume and shape
Probably the least important attribute in practical terms, as even worst case batteries in this regard seem to be able to find a home on some bikes. Shape may be more important than volume, as cells that can be re-arranged to fit the frame space available will be simpler to use than those batteries that come in big, fixed size, blocks, like SLA.
Cost
Importance depends entirely on the means of the purchaser. Some will pay a premium to get exactly the battery they need, others may choose to trade some of the above to get what's affordable to them.
For me, useful capacity, weight and calendar life are the three key attributes, as I doubt I'll ever achieve more than 100 cycles a year on average. My riding is a short daily commute, with an occasional longer ride. I can go three or four days on 10Ah without recharging. Weight was pretty important, as my 'bent handles badly when weighed down. For my initial experiments I didn't want to spend heaps of money, in case things didn't work out, so I opted for cheap batteries. If these work OK then I will look to upgrade to some with a better calendar life as soon as the cheapos start to fade.
I guess we'll all have differing views on the "best" battery, as all of us likely to want different things from one.
Jeremy
Interesting...
