I’ve recently been trying to pay better attention to our battery health. I purchased all new MK batteries a few weeks ago and have been testing them all on the Computerized Battery Analyzer (“CBA”). They all showed pretty poor capacity at first, but that’s to be expected as these batteries need to be “broken in”. The question is, how much breaking-in is necessary to get a reasonable assessment of the battery? In particular, I tested the same battery three times, each time with slightly better results: 13.8 amp-hours, 13.9, and 14.2. (These are the amp hours before it drops below 10.5V). I’m not using the batteries at all between running these tests - just recharging them. Does that match a typical pattern and values that one might expect for new batteries?
What current are you testing the batteries at?
I wish I had data to go with it, but that sounds like the “break in” cycle is working right!
BTW, those aren’t what I would call poor capacity 
I WISH we had batteries like that. Ours are thrashed 
Capacity is related to the testing current, if you are using the 7.5A draw for the test that is actually pretty decent and within the specs of the battery. We try to strive for all 14+ AH at 7.5A but will pass ones in the high 13s. Best i have ever seen on a test is 15.5AH at 7.5A.
I’m using 7.5 amps top run the test.
After the 2023 season, I test all of the batteries that we had used for 2023 and 2022. Those averaged around 16.1 Amp Hours before cross the 10.5V threshold.
So, perhaps those were unusually good batteries and my expectations are too high?
Yeah 16+ seems really good, are those actually 18AH batteries? MK for example has the rated capacity at 15.3Ah when discharging at 3.06A https://www.mkbattery.com/application/files/6615/3436/0928/ES17-12.pdf
7.5A should be lower capacity.
Taking a good look at the MK cycle life graph there seems to be a slight increase in capacity around the ~200 cycle mark (depending on depth of discharge).
These are the standard ES17-12 that AndyMark sells, although I bought them direct from MK Battery.
200-300 discharges seems like a reasonable number that these batteries have experienced, so that likely explains everything. Thanks!
Over the summer I bought a new Powersonic PS-12180 battery for testing, the sole intent being to understand battery “break-in”. I charged it and ran it through our typical CBA V test multiple times until the discharge curves for consecutive tests were identical.
There was a pretty big difference in capacity between the first and second runs. The difference became less with each cycle until cycle number 5, which looked essentially identical to discharge cycle number 4.
TL;DR 5 cycles.
Any chance of data or graphs? Cause, everything is better with a sweet graph!
I’d love to comply, but the laptop the test was run on (this one) has since been wiped and is running Chrome OS Flex. So no sweet graphs this time.
Batteries can require 20-50 cycles to format. This can be lower if cells are built more uniformly. We also don’t know what formatting the manufacturers do ahead of time.
My memory tells me 5-10 cycles before we get ‘peak’ levels of performance. There is no need to do this with a cba, the formatting cycles can be done with drive practice.
From my very limited testing, if you can get the current way up for those formatting cycles, it helps. For most teams, hard practice should do it.
Update: just retested a battery we bought in January and it just test at 16AH so I stand corrected. Guess those formatting cycles really help a decent amount.
They really do.
We talk about formatting cycles a lot, but don’t have a decent simplified explanation floating around CD. Here goes.
When a battery is first assembled different cells are at (slightly) different voltages. The highest voltage cell limits maximum charge state, and the lowest voltage cell limits depth of discharge. As the battery is used the high voltage cell is discharged the most and the low voltage cell is charged the most, and eventually all cells come to the same charge state. This is the formatting process.
As a (very simplified) hypothetical: one cell is 0.05v higher than the rest. Of the total usable range of about 2.2-1.7v= 0.5v that one cell being 50mV too high reduces the battery’s capacity by 0.05/0.5 = ~10% because that cell stops charging at 2.2v and stops charge current from going through the rest of the battery while the rest of the cells are stuck at 2.15V. And the inverse (ish) happens on discharge.
This may seem silly, but why don’t they make SLA batteries with balance leads (like LiPo, ect.)? Users could then externally balance them (charger or dedicated unit).
The float charge part of the charge cycle should balance them out. This can also work on lithium in certain circumstances.
They do! It’s not at all uncommon to see industrial UPS systems that do this with a whole lot of SLA batteries. The magic trick is that it is not done at the individual cell level.
Too expensive for what lead acid batteries are made to do. Unlike lithium based chemistries, a lead-acid cell won’t explode if it is over-charged or over-discharged*, so there isn’t a safety motivation either. Anyone besides a picky FRC team will just put the battery in service and never notice anything.
*Perhaps the most compelling reason to not use lithium batteries in FRC, but I digress.
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