Understanding batteries

[TartApple]

Can anyone point me towards a good resource to understanding batteries.

This is definitely out of my experience so I'd be looking at something that would help me understand how to evaluate the differences of volts, amps, watts, watt hours, recharge cycles, and chemistry.

Thank you

 

[Stefan Mikes]

It is so simple, @TartApple:

Volt (V) = unit of the driving force of the electric current (voltage). Example: 36 or 48 V battery.

Ampere (A) = unit of the electric current, or how much of current flows through the wire (continuously).

Ampere-hour (Ah) = unit of electric charge in the battery. If you have a 16 Ah battery and draw the current of 1 ampere, the battery will discharge after 16 hours.

Watt (W) = unit of power, or the energy spent in a time unit. W = J/s, where Joule is the energy unit. If your motor produces 250 Watts it means it is spending the energy of 250
Joules per second. 1 W is also equal to 1 V * 1 A. So, if your motor produces 250 Watts and the voltage is 36 V, the current flowing from the battery will be 250 / 36 = 6.94 A.
(750 W is around 1 HP) An average cyclist can produce around 100 W with his or her legs. A professional cyclist can produce 300+ Watts with the muscle power.

Watt-hour (Wh) is the unit of energy stored in the battery. It is exactly equal to 3600 Joules. The battery capacity (amount of the energy stored there) is Volt times Ampere-hour. If your battery is 36 V and the battery charge is 16 Ah, then the battery capacity is 36 * 16 = 576 Wh. The same expressed in Joules is 576 Wh * 3600 = 2,073,600 Joules or 2,073.6 kilojoules (kJ). Wh is a practical measure of the battery capacity.

Recharge cycles = how many times the battery was charged from minimum safe capacity (e.g. 5%) to 100%.

For the chemistry, please refer to:

Lithium-ion battery - Wikipedia

en.wikipedia.org

Hope it helps.

 

[TartApple]

Thanks for replying so quickly.

If I'm evaluating this issue in a bike selection, would Watt Hours be the best in the price range I'm looking at.

 

[6zfshdb]

Ravi Kempiaih, one of our well known members, posted this excellent guide for lithium batteries. It should answer many of your questions.

E-Bike Battery Guide

This thread is dedicated for helping new E-bike owners to understand and maintain their batteries in the best possible way. There is a lot of confusion for any new E-bike owner as to how one should treat their batteries: Shop owners may say one thing, online resources may another thing, someone...

electricbikereview.com

 

[TartApple]

Thank you!

 

[indianajo]

Thanks for replying so quickly.

If I'm evaluating this issue in a bike selection, would Watt Hours be the best in the price range I'm looking at.

watt hours correlates to the distance the battery will carry you at an equal assistance level.
Some vendors use amp-hours which for batteries of the same voltage is also a measure of distance. Multiply by nominal voltage to get watt hours wh.
Some especially cheap batteries have an amp limit which is the limit of the peak power available. "350 W" motors typically will peak at 1000 W which is about 20 amps at 48 v. Batteries built of flashlight cells which are very cheap, will not provide that much current. Home battery builders often buy these for bicycles by mistake.
Volts should match the motor & controller you intend to buy. Full charge and empty charge volts are quite different than the nominal voltage rating. 48 v batteries tend to charge to 54.6 v 100% and about 40 v @ 0 %.
Type has to do with chemistry. LiIon is the smallest size for a given capacity (wh), but will catch fire if punctured. LiIon cannot be charged below freezing. LiFePo4 is not as flammable but is getting difficult to buy. LiMn is less dense but is not as flammable. Lead acid or SLA (sealed lead acid) was common 10 years ago but not now, about 1/5 as dense as LiIon.

 

[J.R.]

Can anyone point me towards a good resource to understanding batteries.

This is definitely out of my experience so I'd be looking at something that would help me understand how to evaluate the differences of volts, amps, watts, watt hours, recharge cycles, and chemistry.

Thank you

Battery University

Battery University Homepage

Battery University™ is a free educational website offering hands-on battery information.

batteryuniversity.com

There are sections for all the different chemistries.

Battery Information Table of Contents, Basic to Advanced

Learn about battery technology, battery maintenance and battery life at Battery University

batteryuniversity.com

 

[harryS]

Usually when one purchases an ebike, the manufacturer has matched the battery and motor, so all you need to look for is the AH rating on the battery. Multiply the AH number by nominal battery voltage to get the watt=hours. More watt-hours means more range. At slow speeds (12 mph), you might burn 8-10 WH/mile with pedal assist. At 16-18 mph, that might rise to 15 WH/mile.

People who own do-it-yourself ebikes have to look at the AH rating when selecting the battery and also match the battery to the motor, making sure it can supply the current needed when running the motor at maximum. If the battery cannot supply the current demanded by a motor, it often shuts down, which kind of ruins the ebiking experience. I've knowingly bought batteries that can only supply 15A, and seen them shut down on my 250W bikes which will need 20A if the throttle is used.