Need a primer on batteries.

I'd love to put a 'Batteries for Dummies" article on my site, if anyone's interested in writing and sharing. :)

I'll try to keep this short if I can, about some of the lifepo4 avaliable. I'm not a techie kind of guy, so here is a simple version of some of the choices.

A123 cells. Usually obtained by breaking up 36v milwaukee tool batteries. A very very good battery, but to use them you need to buy a lot of tools, or the batteries alone to make a decent sise pack. Lots of fussing around with charging methods, keeping the pack balanced, and Dealing with avoiding overdischarge, which ruins them. Very high discharge rate.

EV cells. Such as Thundersky, actually aimed at cars and other larger EV's They can make a great pack, but can be hard to find in the smaller sise a bike needs. 20ah is the smallest I have seen of these. And no idea where to actually buy them. Again you have to figure out your own Battery Management System to avoid overdischarge and pack balancing. Lifebattery also falls into this category and should soon be avaliable in 12 ah sise i think. There are also other similar shaped batteries on ebay that should work well on bikes and small motorcycles.

Prismatic cells. This is the kind used in "duct tape packs" such as those offered by Ping on Ebay. These cells are borderline in ability to power a bike. They have a fairly low discharge rate, so smaller sizes of these batteries tend to underpower some bikes. For some of the lower power bikes, these small batteries, such as 10ah are fine, but some bikes in the over 500 watt class have trouble with these low amperage batteries. I have yet to hear of anyone with problems with discharge rate. when using these batteries in the 20 ah sise. A 20 ah prismatic cell battery should be able to do 20 amps continuous discharge rate. That is plenty for unmodified ebikes. They have a bms to protect them in use. These cells cannot be run in paralel or series connections without voiding the warranty. Schottsky diodes must be used if you do. These little foil pouch cells can have problems with the connections on occasion. They need a little protection to survive a crash, or just rough road riding.

Yesa cells. I honestly do not know if these are also prismatic cells, or small sise EV type cells. Either way, they are a high quality cell, and the bms can tolerate parralel and series connections. I have not heard of problems with these batteries in the smaller sises, so if nothing else, the bms may be letting more amps of current flow than with the duct tape kind.

Lipo cells. Not a good idea. they may explode while charging. Ok if you charge outside at all times. Not known to last as long as Lifepo4 is supposed to.

Discharge rates and BMS. The bms is needed to prevent overdischarge and to rebalance the pack if it gets out of balance. If the pack has one undercharged cell in it, that cell may get overdischarged while the others still have power. To prevent this, a good bms monitors the voltage of each individual cell, and shuts off the pack if one cell goes low. If one cell gets completely discharged, is is usually ruined for life. One bad cell in the pack can cause the pack to shut down early all the time. To fix this the bms also attemts to charge all the cells evenly. The ping bms will charge the battery, and if it senses one low cell, it will discharge the battery a little bit, and recharge it. It will do this several times, till the low cell gets a full charge.

Amp hours. A measure of the theoretical capacity of a battery. SLA batteries often fail to deliver all the ah they are rated for. High discharge rates typical of ebikes result in 30% or more of the potential energy not being avaliable unless the rider uses very small ammounts of the power. Some bikes, like Bionx have assitance settings which if set low, may result in much more of the power being delivered. Other kits, like brushed hubs ridden at full speed, may have as much as 50% of the sla amp hours unusable at the high rate of discharge. This is noticeable as voltage sag, which slows sla bikes at some point in the ride. Lithium batteries do not have this problem. A 10ah lithium battery at full throttle, may deliver as much as 9.5 ah before the bms shuts it down, saving a small ammount to keep the pack alive. There is no noticeable voltage sag with lithium, and battery indicators are less usefull since they basicly measure voltage sag.

Cycle life. Generally 200 full discharges for sla max. Most lifepo4 is expected to go 1000 full discharge cycles. Partial descharge cycles extend the life of both sla and lifpo4 batteries. Generally 80% discharge is preferable. The toyota prius nimh is famous for very long battery life. They use a 50% discharge before the engine starts. I usually recomend people buy 20 ah batteries for this reason, and the higher amperage discharge if prismatic cells. There are speculations that 5000 cycles is possibe with partial discharge of lifepo4. Others say in 5 years the lifepo4 battery dies of old age, used or not. We'll see in five years. I expect to have about 1500 cycles by then anyway.

Look up a site called battery university for the real technical info. I could be very confused about a fact or two, thinking I know it.

Little correction: The A123 cells can be had out of the DeWalt packs. Milwaukees are for emoli cells. These are good, too, but don't have the cycle life of LiFePO4.

And regarding the duct-tape packs; yeah, remember that they are also foil-pouch cells, which means that they don't have a hard casing to them. Putting them in something durable is a good idea. And I think they're rated for 1.5C continuous, 2C max continuous, and 3C peak, meaning that a 20A pack could deliver 30A indefinitely, wouldn't have problems with 40A, and could deliver 60A for short periods.

I have a 48V 20Ah duct-tape pack myself that I got for very cheap because of charging issues, and I love it. :D

Thanks Link, I'm definitely weak on the subject of build it yourself packs. But I try to post so others can spend time building and riding bikes. I spent about 200 hours reading threads this spring. A good summary was needed for the nubies. Another thing I got wrong, Ping is not back yet, but he did finally get some batteries ordered last month delivered. Now it seems to be time for a motor shortage. Thanks to guys like me buying two.