I'm the battery "expert" for our team, not because I want to be, but because I have had a lot of experience in my life as an electrician working with them. I want to quote this post again because it has a lot of really great information and add my emphasis to it as being correct.
Quote:
Originally Posted by eugenebrooks
These are Absorbed Glass Mat (AGM) Valve Regulated Lead Acid (VLRA) batteries. The electrolyte is in a saturated glass mat sandwiched between the plates, there is supposed to no (or at least minimal) liquid electrolyte that is loose in the cell. Any hydrogen and oxygen produced in the cell during operation of the battery is supposed to recombine, returning the water to the mat so that it does not dry out. If the gas production rate gets out of the hand the valve releases it when the pressure in the cell gets to high. This can happen with high charge rates, charging a battery that is too warm, or excessive discharge rates that heats the battery. If you put a battery that is too hot (from high current loading) on a charger, it might go into thermal runaway and this can ruin the battery.
If your batteries measured 10.25 volts without load they were more than fully discharged, this limit being 10.5 volts. You should avoid fully discharging the batteries, it shortens their life.
The battery can be operated in any orientation, but upside down is not advised in case the valves release some gas and there is a little loose liquid at the valve. The battery should be vertical when charging.
If you run these batteries too hard, or charge them too fast, they can dry out and die prematurely. A sign of this is excessive heat during use or charging.
We had some minor leaking from the top of one of our batteries a couple of years ago, cleaned it up and load tested it, and it has remained one of our better performers for several years now without any further issues. Clean them up, give them a proper charge, and load test them. If they pass the load test and don't show any further leaking, they will be fine.
We load test at 20 amps load, recording the time they take to reach 11 volts (under the 20 amp load, and note that we don't go all the way to 10.5 volts). Any battery that gets too close to below 1000 seconds, or so, on this test gets pulled from competition service. A typical battery will last 1500 seconds, while a really good one will last close to 2000. We charge overnight using a three stage charger before testing a battery.
Lastly, you might have done everything right and the batteries might have just given out.
That little 18 amp-hour battery has a really hard life in a FIRST robot.
Have fun,
Eugene
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This year, my team started tracking our batteries using a device called the CBA III
http://www.westmountainradio.com/CBA.htm which does testing of a battery automatically. We are able to spot a weak battery ahead of time, as well as document each battery's condition for comparison in the future.
I'm not endorsing the CBA III. It could be better for our purposes if it could do a test with a bit higher discharge rate. But you can do the same thing with any load (large resistor bank, space heater element, car headlamp, etc.) and set up some sort of recording voltmeter to chart the discharge.
The main idea is to test all your batteries on a single, known load, so that you can compare the discharge from a known level (fully charged) to a known level (11.0V is a good point) The time it takes for good batteries should all fall into a certain range and you will be able to identify any outlyers quickly.
I'm not sure what might have caused the leakage the original poster experienced. It could be simply a bad battery, but more likely it was some incident that he is unaware of and will never know, now, that stressed the battery beyond it's limits. In any event, a battery that rests at less than 10.5V is clearly damaged in at least one cell and should not be used.
One of the easiest things a team can do to extend the life of their batteries, which costs nothing to do except for a little education, is to implement a usage-charge-rest cycle. Number all of your batteries. When you use them start at 1. Use 2 next and put 1 on the charger. When you use 3, put 2 on charge. If you have more discharged batteries than chargers, make sure they go on charge again in order. Work all the way through your bank of batteries before starting over again with 1. Always go in order because it leaves the maximum time between uses and maximizes the time after charging for the battery to cool down. (Very important.) When you are at a competition for more than one day, pick up where you left off int the cycle. If the next fresh battery at the end of the previous day was number 4, use it first even though batteries 1,2, and 3 are now charged. This equalizes usage so battery 1 doesn't get overused and all batteries get equal time.
If you find you don't have enough time in competition to keep up with this cycle, it means you don't have enough batteries or chargers. We have 12 batteries and five chargers, which is probably overkill, but I'd recommend at least 6 batteries and 3 chargers as a minimum for a team serious about competing. If you get into the final rounds at a competition, you'll want at least three fully-charged, fully cooled batteries ready and on the field.
A last point: be careful how much you discharge the battery in use. A two-minute match isn't a problem, but practice often stresses a battery more. Watch the battery voltage as you drive and when it dips below 10V change the battery. It's less stressful on the battery and it charges faster with less heating if it is not fully discharged.
We only got up to 12 batteries by getting a few each year. The fact that the older batteries still stand up means we are handling their care properly. We still have some of the dark gray Gelled Electrolyte batteries as well that are 7 years old and still in good shape.
Properly handled, properly stored and charged, and properly mounted, these batteries should never leak a significant amount of liquid.