sla 3x12v12ah losing speed question

[jeohearn]

I am not a technological person and know very little about batteries. (Although I do know that a lifepo4 would cost me between $500-$600 per month and last longer)
After 3-4 months of use, 5 days per week, charging twice daily for a 7 mile one way commute, I am just now experiencing a decrease in speed (of 5 mph) during the final mile of this commute. The commute is relatively flat but there are some minor hills, and the one way to work is a not very noticeable slight uphill grade most of the way. Does this seem reasonable at this point in the batteries life? Is this normal?
Next question: how much longer will this battery last -will it gradually lose speed earlier and earlier in my commute...or will it suddenly just die?
Thanks for your help.
Jeff

 

[Geebee]

They seem to be dying a bit early but, what wattage is the motor, do you pedal much, do you recharge at work, are they good quality batteries, what % do you flatten them each ride?
The above will all affect the life of the batteries, SLA's are really touchy about the way they are used.
They usually die by slowly losing range ie power will drop off earlier.

 

[davespicer]

Although I do know that a lifepo4 would cost me between $500-$600 per month...

Per month? How did you arrive at this conclusion?

 

[grindz145]

My guess is that it is somewhat normal response given your batteries and how much you charge them. With how much you ride, I recommend ditching the lead and going with something better (liFePo4?). If you go with a bigger pack and it's not necessary for you to drain the back as far everyday, the pack will last much longer, no matter what the chemistry. My guess is that your lead was a little undersized for how hard you run them. How many miles are on it total?

The degradation should be somewhat gradual, but it will start degrading faster from here on out until you end up having to peddle it.

I am also wondering what kind of charger your using. I had issues with my PBA because of a charger which didn't charge the lead properly and which lead to an early demise.

 

[Lock]

Hey Joe... What Geebee and grindz said... You say 3-4 months, so split the diff. at 3.5mo x 4.333 wks per mo... times two cycles per 24hrs... `bout 152 cycles so far... SLA is often rated at 300 cycles (one discharge plus one charge) before ya should freshen it up w/new batts BUT only if you discharge down to 20% SOC (state of charge)... and ONLY if the discharge happens over TWENTY HOURS... These are nominal ratings and pretty far from the real world of ebikes, where ya might be discharging your pack in an hour or less. EVen though you may have regular commute charge/recharge habits, ya might also have "events" where ya run the batts to empty, or forget to plug `em in over the weekend, or don't break`em in gently `cause fresh lead is so damn exciting... Or ya have a cheap charger... Maybe it's winter for you now and the lead is a little cooler than in the first few months? All this stuff messes with lead performance.

Yer 3 x 12V 12V pack sums as 36v x 12Ah so 432Whs BUT yah never want to run that down below 20% so really just 346Whs... and REALLY for long(er) life no more than 50% run down is EVen better... So this is where the questions come in about how much you pedal and how fast you go etc... Trying to know what sort of Whs/mile yer burning, so how deeply you are discharging your pack.

Another way to calc things... How many Amps is your charger rated as and how long does it take after a seven mile trip for the charger to read pack full again after you plug in?

Lock