I asked the question about SLA batteries

[Old Timer]

These are the batteries, I asked about the suitability of using them on an E bike New - RITAR 12v 18AH TOP QUALITY lead acid Battery on eBay (end time 12-Mar-10 14:37:26 GMT)

This was the reply

These are designed as float batteries, so you should not aim to deep discharge them. Best way to do this is to charge them up, then do your first run. Record how long / how far you go with a 100% charge.

Once you have this figure, try to keep your usage to 75% of the max discharge. This will help them to last much longer

Always charge after use.

You get about 500 cycles this way.

 

[onmebike]

That's pretty much what rog-london said.

 

[rog_london]

That advice applies to any lead acid batteries. You should avoid fully discharging any of them if you want a decent life expectancy. That's better advice than I usually see, as it allows for the reduced effective capacity due to heavy discharge currents - see below.

Deep-cycle batteries are designed to better survive full discharges, but they all have limited lives if you do. Deep cycle batteries will also recover better if they are over-discharged, i.e. the damage is reduced.

Two other things to bear in mind:

(1) Discharging to 75% of the stated capacity means that it doesn't take long for that capacity to drop so that in effect your 75% becomes 100%. Therefore to eke out the life of a lead acid battery you need to actually reduce the amount of discharge as it ages.

(2) If your discharge current is high your effective capacity will be reduced from the start. A battery's advertised capacity is often at the 20 hour rate, which means no more than a 1 amp discharge current for a 20 AH battery. In an ebike application you'll probably have much less than 20AH to keep the weight down and it's common to exceed 20 amps for short periods and 10 amps average. This can halve the available capacity.

The golden rule is simple - you get the biggest battery you can afford and can manage to lug around to get a good lifetime. You can see why lead acid batteries are not often used in any but the cheapest ebikes as the battery can easily weigh much more than the bike, or you'll need to limit your range, or you'll need to replace them frequently. There really isn't a good compromise.

They're great for milk floats - those aren't designed to do much more than 15mph either, but a hundredweight battery is no great problem and provided they're plugged in at the end of every round they can last for years.

Roger.

 

[NRG]

^^^^^^^^^^^What Rog said!

 

[onmebike]

That advice applies to any lead acid batteries. You should avoid fully discharging any of them if you want a decent life expectancy. That's better advice than I usually see, as it allows for the reduced effective capacity due to heavy discharge currents - see below.

Deep-cycle batteries are designed to better survive full discharges, but they all have limited lives if you do. Deep cycle batteries will also recover better if they are over-discharged, i.e. the damage is reduced.

Two other things to bear in mind:

(1) Discharging to 75% of the stated capacity means that it doesn't take long for that capacity to drop so that in effect your 75% becomes 100%. Therefore to eke out the life of a lead acid battery you need to actually reduce the amount of discharge as it ages.

(2) If your discharge current is high your effective capacity will be reduced from the start. A battery's advertised capacity is often at the 20 hour rate, which means no more than a 1 amp discharge current for a 20 AH battery. In an ebike application you'll probably have much less than 20AH to keep the weight down and it's common to exceed 20 amps for short periods and 10 amps average. This can halve the available capacity.

The golden rule is simple - you get the biggest battery you can afford and can manage to lug around to get a good lifetime. You can see why lead acid batteries are not often used in any but the cheapest ebikes as the battery can easily weigh much more than the bike, or you'll need to limit your range, or you'll need to replace them frequently. There really isn't a good compromise.

They're great for milk floats - those aren't designed to do much more than 15mph either, but a hundredweight battery is no great problem and provided they're plugged in at the end of every round they can last for years.

Roger.

Isn't this pretty typical of Lithium battery's too? I've had many years experience with R/C model flying and Lipo battery's since their introduction. They lose capacity practically from the first charge. Admittedly they get more abuse with most flights running the cells down to the cutoff point set by the esc.
One particular spec sheet I read on sla battery's claimed that, at a 100% discharge rate you get approx 200 cycle's, 50% 500 cycle's and 30% over 1000? Obviously this is under ideal conditions.
I've never achieved anything like 200 cycle's from a lipo used for R/C flight, not in high powered application's. The capacity drops off alarmingly fast.
Tony.

 

[flecc]

Isn't this pretty typical of Lithium battery's too?

Good quality e-bike lithium polymer batteries are far better than this Tony, normally no noticeable loss at 200 charges.

There seems to be quite a lot of confusion regarding RC and e-bike batteries with li-poly often spoken of. Polymer is a type of construction, not a battery chemistry, and when I've asked the chemistry involved in the RC batteries I've yet to receive a straight reply. It's the chemistry that counts most in respect of battery performance.
.

 

[NRG]

.....And also how you care for them when charging. Continual charging to 100% does them no good as does discharging them to 0%...probably why Tony you got such poor life from them in RC use. For long life you need to top n tail the charge / discharge IE 95% max charge and no lower than ~85% DOD. The current Turnigy and Zippy R/C batteries are incredibly robust with great discharge rate capability but they won't last long unless the charge / discharge levels are carefully monitored...this is where a good BMS comes into its own...

 

[onmebike]

.....And also how you care for them when charging. Continual charging to 100% does them no good as does discharging them to 0%...probably why Tony you got such poor life from them in RC use. For long life you need to top n tail the charge / discharge IE 95% max charge and no lower than ~85% DOD. The current Turnigy and Zippy R/C batteries are incredibly robust with great discharge rate capability but they won't last long unless the charge / discharge levels are carefully monitored...this is where a good BMS comes into its own...

The strange thing here is, with R/C batteries the management is external to the battery. The charging is better monitored in my opinion as each cell is balanced individually as charged[dependant on charger] On the discharge side this is not so well managed because the cutoff point set by the electronic speed controller only monitors the pack as a whole and not individual cells e.g. an 11.1v pack may cut off at 9.9v but the cells could be 3.5v, 3.4v and 3.0v.
As you say the dod is the all important factor. Maybe r/c esc's should be improved to help manage dod better or someone could cash in with a bms that fits between battery and esc which does monitor individual cell's. Now that may be a handy tool, if adjustable that could facilitate the use of different battery type's. The cell-log8 goes part way toward achieving this but is only a monitoring and alarm system it doesn't actually cut power.
Cost is the all important factor which is reflected in ebike battery quality. Not necessarily in better cell construction but better management.

 

[NRG]

The Cellog8 can cut power it has an external alarm port that can be used to cut power IE via a brake cutout or by an external relay to cut the battery feed...

The problem with the majority of RC chargers is their fixed maximum charge voltage per cell...there are some that can be user set to a lower voltage and these are the ones to go for...