Battery Preservation
 

Just a question on how to preserve the life of a robot battery:
When the battery is going to be untouched for an extended period of time should the battery be stored at an almost full charge, or an almost empty charge?

Re: Battery Preservation
 

store a lead acid battery fully charged

http://batteryuniversity.com/learn/a...tore_batteries

Re: Battery Preservation
 

There are a number of good articles available, perhaps this one will help?

http://batteryuniversity.com/learn/a...d_acid_battery

However I'll sum it up to say:

1) Fully charge the battery and take it off the charger.
2) Repeat step one every three to four months.
3) When driving/practicing don't drive you battery down to zero charge... change it and charge it before you fully deplete it.

Put your team name and the date on batteries when you receive them. Use your newest batteries for competition (only!) use the older batteries for practice and public performances.

Well, okay... test the new batteries once or twice before the competition, and one year-old batteries (or even older) are good for competition if you take care of them.

Jason

Re: Battery Preservation
 

Store with a full charge, if storing for an entire off-season, plan to top off the charge mid-way through the time it will not be used. Don't drop or handle by the leads, as these things tend to cause things to break inside the battery. Here's a site that has more (we are using sealed lead acid batteries): <http://batteryuniversity.com/learn/a...tore_batteries>.

Re: Battery Preservation
 

Absolutely. There are a lot of things that make sealed lead acid batteries a good choice for use in FIRST robotics. Unfortunately how they handle being left for even modest periods of time in a partially discharged state, is not one of them. Even if you start fully charged, the batteries will have a limited storage life if the charge is not maintained. Because of this, keeping the batteries from deteriorating during the off season is a perennial issue for FIRST teams. The best solutions almost always requires some periodic interaction to refresh the charge at regular periods.

Re: Battery Preservation
 

All great advice but: Anecdotaly speaking (is that even a word)

We have been storing our batteries at full charge for several years and as of last season we were still using three year old batteries in competition (fully tested of course.) without a single battery related failure.

Treat your batteries well and they will return in kind.

Buy one of these CBAIV for load testing (it's a lot of money but they can be shared among a couple teams in your area)

Also purchase one of these Battery Beak, they are invaluable for testing things like internal resistance and overall health, and knowing the state of charge and battery health of a battery before it goes into your robot at competition is great peace of mind.

Re: Battery Preservation
 

It is if you add another "l"
"Anecdotally"

Re: Battery Preservation
 

I came across a post the other day on a battery forum saying put your charger (or even a bank of chargers) on an inexpensive timer set to turn on for 30 minutes every 24 hours. I was wondering how safe/effective that might be.

Re: Battery Preservation
 

Ether,
This recommendation is a poor man's fix to get around leaving the battery connected to a smart charger. The smart chargers generally turn off once full charge is reached and won't restart until power is removed or the battery is disconnected and reconnected. The general practice of topping off the charge every couple of months is then simulated every 24 hours. Light timers that allow turning devices on once a week is a better substitute as long as they are non-dimming types. Not stated yet is to store batteries where they won't be subject to temperature extremes particularly preventing freezing or temperatures above 100 degrees. In other words don't store them in a garage or shed.

Re: Battery Preservation
 

Al/Ether -

Based on our experience, the batteries seem to slowly discharge when hooked up to an unplugged KoP charger... could one of those normal 24-hour timers (or 1-week timers) that basically "unplug" the charger then be of any great use?

It's still a great idea, and one I might use in the future with our battery cart. When we built it, we noticed batteries discharging over night when left plugged in. To get around that, we added some appropriately sized relays between the charger and the battery, and set it up so they would automatically disconnect the two when power was turned off to the cart. Simple and great solution!

Re: Battery Preservation
 

Jon,
I suspect that the charger has some leakage in one of the output components and that is discharging the battery. Using a timer to disconnect from the power line likely won't help that. It will restore the charge though when the charger turns back on. If this takes place over several months, it might shorten the life of the battery.

Re: Battery Preservation
 

Jon, would you be willing/able to run a simple test? Put a small resistor (1 ohm or less¹) in the circuit (as shown in the attachment) and measure the voltage drop across it² with the charger unplugged.


¹ A 1-foot length of #10 gauge solid copper wire is about 0.001 ohm.

² Make sure you measure the drop across the resistor as shown. Do not include the drop across the resistor's connection to the wires on either end.

Re: Battery Preservation
 

Ether - That sounds like an excellent test. It looks like radio shack has some 1 ohm resistors in stock in the area, so I can pick some up before our next meeting and challenge my students to figure out how to design a test to determine the rate of discharge if we hadn't added the relays (all of the students who built the cart and helped solve the problem initially have graduated, so this will be a great excuse to transfer that knowledge forward to new students!). Of course, the solution is pretty straightforward (use the resistor to bridge the terminals on the relay, measure the voltage drop across the resistor)... I just hope none of them are following this thread, or they'll come with the answer too easily!

Expect answers in a week... our next meeting is Monday night.

Re: Battery Preservation
 

It is not likely that the leakage through the output of the charger in it's off-state is more than a few mA, perhaps a few 10's of mA at the most. The 0.001 Ohm shunt resistance would produce a drop of only a few uV which would be pretty difficult to measure without specialized equipment.

You may want to replace the shunt resistance with a DVM set to measure 10's of milliamps. If you don't see anything, set the DVM to a more sensitive range.

Phil

Re: Battery Preservation
 

You may damage your meter if there is a larger current.

With the "voltage drop across a resistor shunt" method, all you risk damaging is the resistor. Set your voltmeter to 12v (or higher) range, then make it more sensitive if needed.