After reading through Battery Testing Data, I think we found the problem with our new batteries that we purchased on the way to Champs last year. We found out the hard way that perhaps new batteries don’t have the capacity of our previous batteries resulting in brownouts and sad faces and verified this behavior using the CBA.
Have you guys experienced issues with MK batteries fresh off the shelf?
2a. What methods do you use to ensure you’re properly priming your battery?
2b. If you prime your batteries just by running them on your robot, doesn’t that put a lot of stress on a new battery (which is ill-advised according to this battery university website)?
I noticed this on the article about priming and formatting:
Formatting occurs during use; deliberate cycling is not recommended as this would wear down the battery unnecessarily.
We all abuse the heck out of these batteries, and most teams understand they are wear items.
So we buy brands known for quality (MK for us but there are others), we assemble them well with crimped lugs and nord-lock washers and proper hardware, we don’t do excessive levels of abuse in operation (mostly stopping practices for swaps sooner than you think is necessary), we test them a few times a year on the CBA, and that’s about it.
yeah I read that as well, just trying to get the batteries in prime condition and ready for competition, and am willing to sacrifice life of the battery to get to the peak performance for a competition.
Last year, swerving and shooting demanded every ounce of life from our battery.
I will say I recall some batteries testing better on later testing. I don’t recall whether the first tests were before or after we redid our cables and connections, and I wasn’t controlling for ambient temperatures either. I just take the number as it comes.
Testing on a CBA will also show a mild voltage rise as the battery comes up to temperature during a run. So my current line of thinking is that for two equal batteries, you’d want to run the one that most recently completed a charge for best performance.
That said, it may just also be that the brushless swerve age has finally pushed us to the upper limit of what a battery this size can produce over 2.5 minutes. I’m suspecting there will be focus in the coming years on how to make robots consume less energy during a match, whether through right-sizing components, better software controls, more focus on maintenance, or a new style of driving. Kind of like how Formula 1 teams adapt to the sport’s limits on fuel and tires (and more recently, spending).
Battery University has the procedure. But it is pretty wishy washy. It suggests 50 cylcles to fully break in. But it says don’t do that because it decreases battery life. I suggest use them lightly for 5-10 cycles. Don’t use heavy loads and don’t fully discharge. Fully charge between cycles. YMMV.
We don’t do anything special but try to avoid going to competition with new batteries.
All 9 comp batteries are lightly cycled 2-3 times on the robot before our first event, we don’t drain them all the way, just a teleop/shoot around simulation or something light.
After the couple cycles, comp batteries are untouched until official event practice matches, we normally zip tie them to the chargers. The only exception is when we do a pre-event or during-event shooter map tune we might pull a comp off, making sure to not cycle it too low.
Batteries are checked for “130%” on the battery beak before being used in a match
This can be adapted to work with fewer comp batteries/charges but I would try to get to at least 3 triple chargers 6-7 comp batteries, 2-3 practice batteries w/ 2-3 more practice off the charger.
We haven’t found the need to purchase new batteries mid-season or before worlds, something I know a lot of other teams with power-hungry robots like ours do.
Mks were back ordered for the first bit of build season and we bought some interstates in case we didn’t get ours in time, we found even our 2 year old MKs (last seasons practice) would run longer than the brand new interstates (conditioned as above).
Edit: Forgot to add if you have enough Comp batteries you should be numbering them and using them in order.
All 6 practice are retired. We only keep 6 of the comps, We can normally identify 2-3 “bad” batteries by the end of the season, maybe high IR or the leads are a little loose. We all retired away (if there are still in pretty good shape) or dispose of.
We still had about 3-4 2019 batteries in our pit this year through IRI. One of them finally died on us in practice the other day (not died but lost alot of capacity, like from 12->9AH on CBA), so I’d say in agreement that 3 years is probably the max. Typically we try to buy about 4 new batteries a year keeping 12 of the “Best” ones (>= 12.0AH at 7.5A testing). We may splurge a little bit if we can this year on more but we are trying to keep our budget healthy and our MK2 swerves are showing their age so new swerves look likely for the upcoming season.
I am glad to see Rev started selling the MK Batteries, just got 4 on our last order and the 2 tested so far have been 13.5 and 14.5AH iirc so looking pretty solid, this should allow us to retire all of our 2019 batteries and run 20-21, 22, and these new “23” ones.
As I posted in another thread we were very surprised to find that two batteries purchased at the same time, sitting on the store shelf next to each other tested so differently on the CBA. Both were better than our old batteries but we really wanted more of the one that tested so much better.
Some might wonder why batteries need this break-in period. It is to balance the batteries cells.
Manufacturing and other variations can lead to different cells starting off at slightly different voltages. When discharging the higher voltage cells are driving the lower voltage cells up, suboptimal to say the least.
A lithium pack I’m working with has a cluster of wonky cells that make this quite visible (near the middle of the lower plot of cell voltages). I was unable to fully charge, or discharge, this pack on it’s first cycle because of this group. They are coming into line as the the battery management system balances them though.
I’ll note that this particular charger, while great at doing what it says (especially long-term maintaining), is absolutely crippled by the inline glass fuses and their poorly implemented connectors. I’ve found half a dozen over the years that teams thought were partially broken with one bank not charging, but it was just the fuse holder falling apart.
Got to keep an eye on them, or replace with some other fuse system.
But what were their date codes? Just because they were sitting side by side doesn’t mean that they were the same age. Not everybody properly rotates their stock and if they store just does moderate in volume in that particular model, a battery can sit around the store sometimes for months.